Citation Nr: 26002145 Decision Date: 02/17/26 Archive Date: 02/17/26 DOCKET NO. 14-23 306 DATE: February 17, 2026 ORDER Entitlement to service connection for sleep apnea is denied. FINDING OF FACT The evidence weighs persuasively against finding that the Veteran has sleep apnea that is related to his active military service, to include exposure to herbicide agents therein, or is proximately due to, the result of, or aggravated by his service-connected ischemic heart disease. CONCLUSION OF LAW The criteria for entitlement to service connection for sleep apnea have not been met. 38 U.S.C. §§ 1110, 1131, 5107; 38 C.F.R. §§ 3.102, 3.310. REASONS AND BASES FOR FINDING AND CONCLUSION The Veteran served on active duty in the United States Army from August 1968 to May 1970, including service in the Republic of Vietnam. The Board sincerely thanks the Veteran for his service to our country. This matter comes before the Board of Veterans' Appeals (Board) from a February 2011 rating decision by a Department of Veterans Affairs (VA) Regional Office (RO). This claim was previously before the Board in December 2019 and January 2021, when it was remanded for further development. It was again before the Board in September 2021, when the claim was denied. The Veteran appealed the Board's decision to the U.S. Court of Appeals for Veterans Claims (Court). In a July 2022 Order, granting a July 2022 Joint Motion for Remand (Joint Motion I), the Court vacated and remanded the September 2021 Board decision consistent with the terms of the Joint Motion. The case then returned to the Board in December 2022, when the Board remanded the sleep apnea service connection issue for additional development to comply with the directives of Joint Motion I. The case returned to the Board for further appellate review and was denied by an October 2023 Board decision. The Veteran appealed the Board's October 2023 decision to the Court. In an October 2024 Order, granting an October 2024 Joint Motion for Remand (Joint Motion II), the Court vacated and remanded the October 2023 Board decision consistent with the terms of Joint Motion II. In March 2025, the sleep apnea issue on appeal again returned to the Board for further appellate review and was remanded for additional development to comply with the directives of Joint Motion II. In September 2025, the sleep apnea issue again returned to the Board for further appellate review and was remanded again for corrective development to adequately complete the development previously directed. The case has now returned to the Board once again for further appellate review. The Veteran testified before the undersigned at a Board hearing in September 2019. A transcript of that hearing is of record. ? Prefatory Note on Compliance with Multiple Concerns of Joint Motions Preliminarily, the Board takes a moment here to outline how its decision in this case acknowledges and responds to the various concerns raised in the two Court-endorsed Joint Motions. This discussion is intended to clarify the Board's response to the several concerns expressed in the Joint Motions in advance of the Board's main analysis of the merits of the case. Joint Motion II discussed a need for the Board's analysis of the history of sleep apnea to "address evidence 'which may indicate in-service onset of his daytime fatigue.' Specifically, Appellant pointed to a July 1970 service treatment record (STR)," and this evidence "stated the 'patient returned from Vietnam on 5/24/70 and was discharged from the army on the same date' and that he 'had been over there for about a year and generally he had felt well but had felt somewhat tired and run down during the last few weeks over there[.]'" This concern of Joint Motion II has now been addressed. VA has developed a November/December 2025 VA medical opinion in which the authoring clinician's December 2025 addendum directly addressed the fact that the evidence shows that the Veteran "was seen within a few months from separation for, '... reports of fatigue in Vietnam.'" The VA examiner discusses that the contemporaneous documentation of that treatment shows that "The cause of the veteran's fatigue ... was due to an acute pulmonary lung infection (pneumonia) which was resolved with antibiotic treatment." This competent medical evidence informs the Board's understanding in this decision that the Veteran's in-service fatigue has been medically attributed to acute pneumonia, and this symptomatology was accounted for in the November/December 2025 VA medical opinion's determination that the obstructive sleep apnea did not have onset or causation during service. Joint Motion II also discussed a need for the Board to "address whether the presence of nasal congestion in June and July 1970 ... may have been related to service and Appellant's OSA." This concern of Joint Motion II has also now been addressed in connection with the November/December 2025 VA medical opinion in which the authoring clinician's December 2025 addendum directly addressed the fact that the evidence shows that the Veteran "was seen within a few months from separation for, 'nasal congestion ... in Vietnam.'" The VA examiner discusses that the contemporaneous documentation of that treatment shows that "The cause of the veteran's ... nasal congestion was due to an acute pulmonary lung infection (pneumonia) which was resolved with antibiotic treatment." This competent medical evidence informs the Board's understanding in this decision that the Veteran's in-service nasal congestion has been medically attributed to acute pneumonia, and this symptomatology was accounted for in the November/December 2025 VA medical opinion's determination that the obstructive sleep apnea did not have onset or causation during service. Joint Motion II discussed a related concern regarding an argument "that the August 2020 medical .... examiner's opinion was deficient because they did not address the part of the July 1970 STR that stated Appellant had "a lot of nasal congestion." This concern has now been addressed by the development of the November/December 2025 VA medical opinion that informs the Board's analysis in this decision such that the Board does not rely upon the August 2020 VA examiner's opinion in connection with analyzing this theory of entitlement. With regard to the theory of entitlement to service connection based upon direct in-service incurrence or onset of obstructive sleep apnea, the Board's current analysis in this decision does not rely upon the August 2020 VA medical opinion to inform its determination. Therefore, any deficiencies in the August 2020 VA medical opinion's discussion of in-service events in this regard have no impact upon the Board's current decision. Joint Motion II also discussed another related concern regarding the fact that a May 2023 VA examiner's report "did not discuss the 1970 STRs (noted above)" that document the Veteran's report of nasal congestion and fatigue around the time of the conclusion of his active duty service. This concern has now been addressed by the development of the November/December 2025 VA medical opinion that informs the Board's analysis in this decision such that the Board does not rely upon the May 2023 VA examiner's opinion in connection with analyzing this theory of entitlement. With regard to the theory of entitlement to service connection based upon direct in-service incurrence or onset of obstructive sleep apnea, the Board's current analysis in this decision does not rely upon the May 2023 VA medical opinion to inform its determination. Therefore, any deficiencies in the May 2023 VA medical opinion's discussion of in-service events in this regard have no impact upon the Board's current decision. The Board notes that its decision in this case does rely upon a May 2023 VA medical opinion to inform consideration of a theory of entitlement based upon in-service toxic exposure, but this is unaffected by the concerns of the Joint Motions. The new November/December 2025 VA medical opinion informs the Board that the Veteran's in-service fatigue and nasal congestion were attributed to his acute pneumonia unrelated to the etiology of his obstructive sleep apnea. This case involves no suggestion, including in the concerns of the Joint Motions, that the Veteran's acute pneumonia in 1970 presents a basis for linking the Veteran's obstructive sleep apnea to his in-service toxic exposures. The May 2023 VA medical opinion remains adequate to inform the Board's analysis as to whether the Veteran's obstructive sleep apnea is otherwise attributable to the in-service toxic exposures. The older Joint Motion I, to the extent that it concerns the sleep apnea issue, presents a concern that "the August 2020 VA opinion did not adequately account for Appellant's medical history." This is discussed with attention to the fact that "the record reflects symptoms and suspected OSA prior to the 2006 diagnosis that the VA examiner relied upon," noting March and May 2002 private referrals for "a sleep evaluation," and that the "Appellant reported symptoms of significant fatigue in 2001, five years earlier than the date the VA examiner relied upon." This concern is presented specifically in consideration of the August 2020 VA medical opinion's conclusion relating to the theory of entitlement to service connection on a direct basis. This concern has been resolved by the December 2025 VA addendum medical opinion. Unlike the August 2020 VA medical opinion, the December 2025 addendum VA medical opinion does not rely upon citation of a 2006 date of earliest diagnosis in its reasoning. The December 2025 addendum VA medical opinion does not rely upon any specific date of onset of sleep apnea. Rather, the December 2025 addendum VA medical opinion's analysis stands on the medical reasoning that the facts for the Veteran's documented in-service (and proximately post-service) medical history present no valid basis for finding that obstructive sleep apnea was caused or had onset during his active duty service. As noted above, with regard to the theory of entitlement to service connection based upon direct in-service incurrence or onset of obstructive sleep apnea, the Board's current analysis in this decision does not rely upon the August 2020 VA medical opinion to inform its determination. Therefore, any deficiencies in the August 2020 VA medical opinion's discussion of in-service events in this regard have no impact upon the Board's current decision. Joint Motion II also discussed a concern regarding an argument "that the March 2021 medical opinion was inadequate .... as to the secondary service connection opinion because the examiner found no evidence that coronary artery disease was a risk factor of OSA, while relying on medical literature that noted that the 'prevalence of OSA is also increased in patients with cardiovascular disease.'" The Board notes that the March 2021 VA medical opinion is only an addendum portion of an August 2020 / March 2021 VA medical opinion that, when read in its entirety, does indeed explain that the medical literature showing a "prevalence" of OSA in patients with cardiovascular disease does not indicate that coronary artery disease causes obstructive sleep apnea. Regardless, the Board has taken care to complete development, with two remands of the case ensuring completion, to ensure clarity in the evidence and to ensure demonstrative compliance with the requirements of Joint Motion II. The resulting June 2025 and November 2025 VA medical opinions are adequate to inform the Board's analysis regarding the secondary service connection theory of entitlement in this case. The June 2025 and November 2025 VA medical opinions do not present any apparent tensions between their cited evidence and their conclusions in the manner Joint Motion II is concerned with in its discussion of the March 2021 VA medical opinion. Moreover, while the June and November 2025 VA medical opinions are adequate and sufficient to inform the pertinent analysis on their own, it is notable that when the March 2021 addendum VA medical opinion is read together with the August 2020 portion of the opinion, that evidence would also be adequate and sufficient. It is apparent that the author of the August 2020 / March 2021 opinion explained that the data showing "prevalence" does not indicate that coronary artery disease causes obstructive sleep apnea. Joint Motion II states that the Board must address "the express arguments set out in the November 2022 SOI [statement of issues]." These have been substantially addressed in the Board's responses to Joint Motion II's explicit identification of concerns above. 1. Entitlement to service connection for sleep apnea is denied. Service connection may be granted for disability due to disease or injury incurred in or aggravated by active military service. 38 U.S.C. § 1110; 38 C.F.R. §§ 3.303, 3.304. Service connection may also be granted for any disease diagnosed after discharge when all the evidence, including that pertinent to service, establishes that the disease was incurred in service. 38 C.F.R. § 3.303. To substantiate a claim of service connection, there must be evidence of: (1) a current disability; (2) a disease, injury, or event in service; and (3) a nexus or causal relationship between the claimed disability and the disease, injury, or event in service. Shedden v. Principi, 381 F.3d 1163, 1166-67 (Fed. Cir. 2004). In some circumstances, certain enumerated diseases associated with exposure to certain herbicide agents will be presumed to have been incurred in service even though there is no evidence of that disease during the period of service at issue, unless there is affirmative evidence to establish that the disease is due to an intercurrent injury or disease. 38 U.S.C. § 1116(a); 38 C.F.R. §§ 3.307(a)(6), 3.307(d)(1), 3.309(e). A veteran who served in the Republic of Vietnam during the Vietnam era shall be presumed to have been exposed during such service to an herbicide agent, unless there is affirmative evidence to establish that the veteran was not exposed to any such agent during that service. 38 U.S.C. § 1116(f); 38 C.F.R. § 3.307(a)(6). Diseases associated with such exposure are listed in 38 U.S.C. § 1116(a)(2) and 38 C.F.R. § 3.309(e). (The Board notes that Congress has revised 38 U.S.C. § 1116(a)(2) to include three additional diseases as due to herbicide agent exposure: (1) Parkinsonism, (2) bladder cancer, and (3) hyperthyroidism. See William M. (Mac) Thornberry National Defense Authorization Act for Fiscal Year 2021 ("NDAA FY 21"), Pub. L. No. 116-283 § 9109, Stat. (2021).) The Secretary of VA has determined that there is no positive association between exposure to herbicides and any other condition for which the Secretary has not specifically determined that a presumption of service connection is warranted. See Notice, 75 Fed. Reg. 32540 (June 8, 2010). The Veteran's DD Form 214 reflects that he served in the Republic of Vietnam from May 31, 1969, to May 24, 1970. Thus, exposure to herbicide agents during his service is presumed. See 38 C.F.R. § 3.307(a)(6)(iii). Although OSA is not among the list of presumptive herbicide-related diseases enumerated in 38 U.S.C. § 1116(a)(2) and 38 C.F.R. § 3.309(e), service connection is still available on a direct basis. See Combee v. Brown, 34 F.3d 1039, 1043-1044 (Fed. Cir. 1994). A veteran can receive compensation via secondary service connection, which can be established when a disability is shown to be proximately due to or the result of a service-connected disease or injury. 38 C.F.R. § 3.310. To be awarded secondary service connection, there must be evidence sufficient to show: (1) that a current disability exists; and (2) that the current disability was either (a) caused by or (b) aggravated by a service-connected disability. Id.; Allen v. Brown, 7 Vet. App. 439, 448 (1995) (en banc). To be service connected on a secondary basis under a causation theory, the primary disability need not be service-connected, or even diagnosed, at the time the secondary condition is incurred. Frost v. Shulkin, 29 Vet. App. 131, 138 (2017) (holding that there was not a temporal requirement inherent in 38 C.F.R. § 3.310(a) for claims for service connection on a secondary basis). Obesity may act as an "intermediate step" between a service-connected disability and a current disability that may be service-connected on a secondary basis under 38 C.F.R. § 3.310(a). Id. See also Walsh v. Wilkie, 32 Vet. App. 300 (2020); Garner v. Tran, 33 Vet. App. 241 (2021). In Walsh, the United States Court of Appeals for Veterans Claims (Court) endorsed the guidance provided in the General Counsel's opinion for adjudicating these claims. To decide entitlement to secondary service connection in such cases, the Board is required to resolve: (1) whether the service-connected disease or injury caused the veteran to become obese or aggravated obesity; (2) if so, whether the obesity caused or aggravated as a result of the service-connected disability was a substantial factor in causing the claimed secondary disability; and (3) whether the secondary disability would not have occurred but for obesity caused or aggravated by the service connected disease or injury. Garner, at 247. The Court has held that proper interpretation of VAOPGCPREC 1-2017 requires consideration of both proximate causation and aggravation in its analytical framework. Walsh v. Wilkie, 32 Vet. App. 300, 305 ("the principles contained in § 3.310 make any distinction in G.C. Opinion 1-2017 between causation and aggravation legally untenable.") When there is an approximate balance of positive and negative evidence regarding the merits of an issue material to the determination of the matter, the benefit of the doubt in resolving each such issue shall be given to the claimant. 38 U.S.C. § 5107 (b); 38 C.F.R. § 3.102. When all of the evidence is assembled, VA is responsible for determining whether the evidence supports the claim or is in approximate balance, with the veteran prevailing in either event, or whether the evidence weighs persuasively against the claim, in which case the claim is denied. Gilbert v. Derwinski, 1 Vet. App. 49, 55 (1990). The Board notes that it has reviewed all of the evidence properly of record for this appeal, with an emphasis on the evidence pertinent to the issue on appeal. Although the Board has an obligation to provide reasons and bases supporting this decision, there is no need to discuss, in detail, every piece of evidence of record. Gonzales v. West, 218 F.3d 1378, 1380-81 (Fed. Cir. 2000). Hence, the Board will summarize the relevant evidence, and the Board's analysis below will focus specifically on what the evidence shows, or fails to show, as to the claim. The Veteran contends that he is entitled to service connection for OSA as secondary to service-connected coronary artery disease, including with obesity as an intermediary step. See June 2014 VA Form 9; May 2021 Appellate Brief. The Board acknowledges the Veteran's contention that his obesity serves as an intermediate step between service-connected ischemic heart disease and obstructive sleep apnea. However, the weight of the evidence is not sufficient to demonstrate nor indicate that the Veteran's service-connected ischemic heart disease caused him to become obese or aggravated his obesity. For instance, while a January 2011 VA examiner stated that the Veteran's ischemic heart disease limits his ability to participate in strenuous activity, a February 2020 exercise test showed that exercise capacity was fair, and numerous treatment records show that the Veteran was encouraged to exercise. See, e.g., October 2018 Private Treatment Record. Thus, a VA examination or a medical opinion addressing obesity as an intermediate step is not warranted. 38 U.S.C. § 5103A (d); 38 C.F.R. § 3.159 (c)(4)(i); McLendon v. Nicholson, 20 Vet. App. 79, 81-82 (2006). Therefore, obesity does not provide an adequate basis for service connection as an intermediate step. The Board now turns its attention to the question of whether the Veteran's service-connected coronary artery disease presents a basis for an award of secondary service connection for obstructive sleep apnea (other than the theory featuring obesity as an intermediate step). The August 2020 VA examiner opined that the Veteran's sleep apnea is less likely than not caused or aggravated by his service-connected ischemic heart disease. The clinician acknowledged recent evidence-based medical information, which noted an association between (among other conditions) cardiovascular disease and obstructive sleep apnea. The clinician clarified, however, that even though the prevalence of obstructive sleep apnea is increased in connection with the conditions included in the article, a causative nexus has not been established. The clinician further reasoned that review of the most current evidence-based medical literature does not show any pathophysiologic evidence to correlate ischemic heart disease as a cause/etiology and/or an aggravating factor of obstructive sleep apnea, or to support any physical or emotional factors from ischemic heart disease that influence obstruction of the airway in obstructive sleep apnea. The clinician concluded that the Veteran's sleep apnea is less likely than not proximately due to or the result of the Veteran's ischemic heart disease, and that his obstructive sleep apnea is less likely than not aggravated by his service-connected ischemic heart disease. In a March 2021 addendum opinion, the clinician considered the article described in the January 2021 Board decision, "Obstructive sleep apnea and ischemic heart disease in southwestern US veterans: implications for clinical practice." C.M. Baldwin, I.R. Bell, S. Guerra and S.F. Quan, Sleep Breath, 2005 Sept.; 9(3): 111-8. The clinician stated that the study shows an already known association of obstructive sleep apnea as a risk factor for coronary artery disease. The clinician opined that the study does not show evidence to support a finding that coronary artery disease is a risk or aggravating factor for obstructive sleep apnea and concluded that the Veteran's sleep apnea is less likely than not caused by his service-connected heart disability of ischemic heart disease. Joint Motion II identified that "the Board ... failed to address Appellant's argument in the SOI that the March 2021 medical opinion was inadequate." In this regard, "in the SOI Appellant argued that the March 2021 VA medical opinion was inadequate as to the secondary service connection opinion because the examiner found no evidence that coronary artery disease was a risk factor of OSA, while relying on medical literature that noted that the 'prevalence of OSA is also increased in patients with cardiovascular disease.'" Joint Motion II refers to an argument that the March 2021 VA medical opinion was inadequate due to essentially an unresolved point of perceived tension between (1.) the conclusion that there was no evidence that coronary artery disease was a risk factor for obstructive sleep apnea, and (2.) the citation of medical evidence indicating an increased "prevalence" of obstructive sleep apnea in patients with cardiovascular disease. The Board responds to this concern by noting, first, that "prevalence" is not synonymous with any indication of causation and does not imply any etiological link. It would be logically incorrect to characterize a prevalence of obstructive sleep apnea among patients with cardiovascular disease as logically indicative that coronary artery disease is a risk factor causing obstructive sleep apnea. This is explained by the August 2020 / March 2021 VA medical opinion, reading the two sections together (both by the same author addressing the same matter). As discussed above, as in the Board's vacated October 2023 decision, the clinician acknowledged recent evidence-based medical information, which noted an association between (among other conditions) cardiovascular disease and obstructive sleep apnea. The clinician clarified, however, that even though the prevalence of obstructive sleep apnea is increased in connection with the conditions included in the article, a causative nexus has not been established. Neither the Board nor the Court-endorsed Joint Motions have found that the August 2020 / March 2021 VA medical opinion's discussion of the prevalence of obstructive sleep apnea among patients with cardiovascular disease is genuinely inadequate or non-probative. Rather, Joint Motion II identified a need for the Board to provide greater reasons and bases responding to the fact that "Appellant argued that the March 2021 VA medical opinion was inadequate as to the secondary service connection opinion." The Board has since directed development of further medical opinion evidence on the matter to afford the Veteran's contentions every consideration, to ensure clarity in the evidence, and to ensure demonstrative compliance with Joint Motion II. Nevertheless, the Board finds that when both portions of the August 2020 / March 2021 VA medical opinion are read together, the VA medical opinion is adequately clear that the noted prevalence does not indicate that the coronary artery disease may be considered a cause of obstructive sleep apnea. Affording significant consideration to the Veteran's concerns endorsed by Joint Motion II, the Board directed new evidentiary development in March 2025. The development directed in the March 2025 remand was in response to the concern that the March 2021 addendum portion of the opinion, if read in isolation from the August 2020 section, could arguably be considered somewhat unclear with regard to how the cited evidence of increased prevalence relates to the conclusion that coronary artery disease is not a risk factor for obstructive sleep apnea. The Board's March 2025 remand directed the development of a new VA medical opinion to address the issue once again in a manner that may more clearly avoid any appearance of unresolved tension between a conclusion and cited evidence. Then, the Board's September 2025 remand directed corrective development to ensure that the new medical opinion was fully complete with regard to the aggravation theory. In accordance with the March 2025 and September 2025 Board remands, VA has developed new medical opinions to once again address these concerns. A June 2025 VA medical opinion presents the conclusion that the Veteran's obstructive sleep apnea has not been caused by coronary artery disease in this case. The June 2025 VA examiner explained: The conditions of Severe obstructive sleep apnea and coronary artery disease status post coronary artery bypass graft are not medically related. The severe obstructive sleep apnea is a separate entity entirely from the coronary artery disease status post coronary artery bypass graft and unrelated to it. A thorough review of medical literature failed to demonstrate a causal relationship. A nexus has not been established. This June 2025 VA medical opinion addresses the causation aspect of this theory of entitlement with no suggestion of an internal unresolved conflict between cited evidence and conclusions. The Board further finds that there is no logical contradiction between the June 2025 VA medical opinion's conclusion that coronary artery disease does not cause obstructive sleep apnea and any indication of an increased prevalence of obstructive sleep apnea in patients with cardiovascular disease in prior evidence. The Board finds that the June 2025 VA medical opinion is internally consistent and uncontradicted. It is further competent and adequate evidence probatively indicating that the Veteran's obstructive sleep apnea has not been caused by his coronary artery disease. Because the June 2025 VA medical opinion did not additionally include an adequate discussion of the aggravation aspect of this secondary service-connection theory, the Board's September 2025 remand directed development of a further VA medical opinion addressing this aggravation aspect. The resulting November 2025 VA medical opinion addresses the aggravation question by finding that it is unlikely that the obstructive sleep apnea has been aggravated by the service-connected coronary artery disease. In this regard, the November 2025 VA medical opinion explains: "A review of available STRs/C-files does not support evidence of recurrent chronic symptomatology which documents aggravation of sleep apnea from cardiovascular disease." The November 2025 VA medical opinion goes on to explain that, with attention to the Veteran's medical records and the medically acceptable measure of severity for obstructive sleep apnea, "There is no objective documentation supporting sleep apnea aggravated beyond its natural progression by cardiovascular disease." The Board finds that the November 2025 VA medical opinion is internally consistent and uncontradicted. It is further competent and adequate evidence probatively indicating that the Veteran's obstructive sleep apnea has not been aggravated by his coronary artery disease. The Board finds that the June 2025 (causation) and November 2025 (aggravation) medical opinions present competent and probative evidence adequately informed by the record, citing medical principles, and supported by clear and persuasive explanations of rationale. These medical opinions weigh persuasively against finding entitlement to service connection for obstructive sleep apnea as secondary to coronary artery disease in this case. There is no contrary probative evidence of record on this point, and the June 2025 and November 2025 VA medical opinions are, considered alone, adequate to inform this matter. The Board observes, while acknowledging the Veteran's arguments recognized in Joint Motion II arising from an arguable degree of unclarity in reading the March 2021 addendum VA medical opinion in isolation, reading the combined August 2020 / March 2021 VA medical opinion further weighs against finding entitlement to service connection for obstructive sleep apnea as secondary to coronary artery disease in this case. To the extent that it addresses whether the Veteran's sleep apnea has been caused or aggravated by his service-connected heart disease, the combined August 2020 / March 2021 VA medical opinion presents a competent expert's probative evidence adequately informed by the record, citing medical principles, and supported by clear and persuasive explanations of rationale. While the Veteran believes his sleep apnea is proximately due to, the result of, or aggravated beyond its natural progression by, his service-connected ischemic heart disease, he has not been shown to be competent to provide a nexus opinion regarding this issue. The issue is medically complex, as it falls outside the realm of common knowledge of a layperson. Therefore, it is outside the competence of the Veteran in this case because the record does not show that he has the skills or medical training to make such a determination. Jandreau v. Nicholson, 492 F.3d 1372, 1377 n.4 (Fed. Cir. 2007); see also Kahana v. Shinseki, 24. Vet. App. 428 (2011). Consequently, on the matter of entitlement to service connection for obstructive sleep apnea as secondary to heart disease, the Board finds more probative weight in the June 2025 and November 2025 VA medical opinions, which are adequate competent evidence probatively informing the Board's review of these matters. (The Board furthermore finds that the combined August 2020 / March 2021 VA medical opinion further weighs against this theory of entitlement.) The Board now turns to the direct theory of entitlement that has been raised in this case, assessing whether the Veteran's obstructive sleep apnea was directly caused or had onset during his active duty service. The Veteran's service treatment records (STRs) do not show complaints of or treatment for sleep apnea. On his May 1970 Separation Report of Medical History, the Veteran denied having had frequent trouble sleeping. The August 2020 VA medical opinion additionally addressed the question of whether the Veteran's sleep apnea is etiologically linked to his military service on a direct basis. However, Joint Motion I explains that the August 2020 VA medical opinion did not adequately account for the Veteran's medical history. Joint Motion I describes that the August 2020 VA examiner based a negative nexus opinion on the silence of service treatment records concerning the claimed condition, the Veteran's 1970 date of separation from service, and an understanding that the evidence shows a first diagnosis of sleep apnea in 2006. Joint Motion I points to March and May 2002 private treatment records documenting that the Veteran was referred for a sleep evaluation and the Veteran's October 2001 report of significant fatigue. It explains that the record reflects symptoms and suspected sleep apnea prior to the 2006 date of diagnosis that the August 2020 VA examiner relied upon. Joint Motion I's concern (to the extent of addressing this sleep apnea issue) specifically related to the August 2020 VA examiner's analysis leading to the conclusion that "it was less likely than not that the OSA was related to service." In December 2022, the Board remanded this matter to obtain a medical opinion that addresses the question of a possible nexus between the Veteran's sleep apnea and his military service with attention to the March 2002 and May 2002 private treatment records showing the Veteran's referral for a sleep evaluation, as well as the Veteran's October 2001 report of significant fatigue. In May 2023, the Veteran was afforded a VA examination with medical opinions addressing the questions pertinent to whether the Veteran's sleep apnea is etiologically linked to an in-service event or exposure (or other manner of in-service causation). The May 2023 VA medical opinion concludes that the Veteran's sleep apnea is "less likely than not (likelihood is less than approximately balanced or nearly equal) incurred in or caused by" the Veteran's military service. The VA examiner explains the analytical rationale for this conclusion. The VA examiner noted "documentation of the Veteran's symptoms of fatigue in 2001," and that "In March and May of 2002 medical notes mention a sleep apnea evaluation but none were performed until 2006." The VA examiner discussed that at the time of the 2001 fatigue, the Veteran "had low testosterone levels, weight gain and 'an overeating and quality food disorder.'" The VA examiner explained: "In 2001 the Veteran's fatigue could have been due to low testosterone or obstructive sleep apnea. However, when his sleep study was conducted five years later, he had lost 80 lbs. But still weighed 285 lbs. So he was likely obese in 2001 as well as 2002, and likely had obstructive sleep apnea." Accepting that the Veteran likely had the sleep apnea as early as 2001, the VA examiner's analysis goes on to note that "[h]is service treatment records did not report any problems associated with sleep or daytime somnolence, and at the time of discharge his weight was 160 lbs. (BMI 22)." The VA examiner then states: "Because of the marked increase in body weight since active duty and the impact of obesity on OSA, it is less likely as not that the Veteran[']s obstructive sleep apnea was related to military service." The Court-endorsed Joint Motion II explains concerns regarding the May 2023 VA medical opinion: the Board provided an inadequate statement of reasons or bases for finding the May 2023 VA examiner's opinion was probative.... In the examination notes, the examiner found that the "[s]eparation exam showed no findings related to the claimed condition."... However, the examiner did not discuss the 1970 STRs... in which it was noted that Appellant had "a lot of nasal congestion" upon admission and "had been over there [Vietnam] for about a year and generally had felt well but had felt somewhat tired and run down the last few weeks over there[.]"... The Board did not adequately explain its finding that the May 2023 examination was probative in light of the fact that the examiner did not address the June and July 1970 STRs. Joint Motion II discusses this concern in connection with a further need for the Board to "address evidence 'which may indicate in-service onset of his daytime fatigue.' Specifically, Appellant pointed to a July 1970 service treatment record (STR)," and this evidence "stated the 'patient returned from Vietnam on 5/24/70 and was discharged from the army on the same date' and that he 'had been over there for about a year and generally he had felt well but had felt somewhat tired and run down during the last few weeks over there[.]'" The Board notes that the June and July 1970 records identified above as "STRs," or service treatment records, pertain to a period shortly after the Veteran's separation from active duty service. A March 1971 VA examination report summarizes the Veteran's history around this time: "In May of 1970[,] two weeks after his discharge from the service, he.... had pulmonary complaints at this time. He was hospitalized at Kerrville VA Hospital from 6-26-70 to 7-9-70 with a right lung abscess." The Board notes that prior to the right lung abscess diagnosis, the Veteran's symptoms were suspected to be sinusitis, including as documented in July 1970 records. Joint Motion II also identified: "Appellant argued that the August 2020 direct medical opinion was inadequate insofar as it did not adequately address whether the presence of nasal congestion in June and July 1970, which was noted one to two months upon separation from service, may have been related to service and Appellant's OSA." Joint Motion II notes that "Appellant provided in his SOI that the August 2020 medical examiner noted that ['N]asal congestion confers an approximately two-fold increase in the prevalence of OSA compared with controls, regardless of the cause.'" Joint Motion II further discussed that "Appellant argued that the examiner's opinion was deficient because they did not address the part of the July 1970 STR that stated Appellant had 'a lot of nasal congestion.'" With regard to addressing the direct theory of service connection (the theory that the Veteran's obstructive sleep apnea was caused or incurred during his active duty service, including in connection with the above-discussed congestion and fatigue), the Board's March 2025 and September 2025 remands directed development to more adequately address the case. This development ultimately resulted in a November 2025 VA medical opinion with a December 2025 addendum medical opinion. The Board finds that the November/December 2025 VA medical opinion is adequate to inform the Board's analysis of the direct theory of service connection; thus, the Board need not rely upon the August 2020 or the May 2023 VA medical opinions to inform analysis of this theory of entitlement (except to the limited extent to which the May 2023 VA medical opinion informs consideration of the theory of entitlement based upon toxic exposure, discussed below and unaffected by the Joint Motions). The November 2025 portion of the VA medical opinion presents the conclusion that the Veteran's obstructive sleep apnea "was less likely than not ... incurred in or caused by the claimed in-service injury, event or illness." In the December 2025 addendum portion of the VA medical opinion, the same authoring clinician directly addressed the fact that the evidence shows that the Veteran "was seen within a few months from separation for, 'nasal congestion and reports of fatigue in Vietnam.'" The VA examiner discusses that the contemporaneous documentation of that treatment shows that "The cause of the veteran's fatigue and nasal congestion was due to an acute pulmonary lung infection (pneumonia) which was resolved with antibiotic treatment." With full consideration of this evidence, the VA examiner explained: "Although August 2020 VA examination reports note that Nasal congestion confers an approximately two-fold increase in the prevalence of OSA, the veteran's nasal congestion was in acute setting of pneumonia which resolved.... [I]t is not sufficient to cause OSA on its own." The Board finds that the December 2025 VA addendum medical opinion adequately explains the medical conclusion that the Veteran's congestion / acute pneumonia diagnosed and treated shortly after the Veteran's separation from active service in 1970 did not cause the Veteran's obstructive sleep apnea. The December 2025 addendum VA medical opinion remarked that nasal congestion "may unmask" or "worsen existing sleep-disordered breathing...." This is consistent with the point discussed in Joint Motion II regarding evidence that nasal congestion is associated with an increased "prevalence" of obstructive sleep apnea. The Board notes that such a "prevalence" is not indicated to reflect any manner of causation, and the December 2025 addendum VA opinion's explanation accounts for the "prevalence" in its discussion of nasal congestion unmasking or worsening existing sleep apnea in certain cases. The December 2025 addendum VA medical opinion is clear that the Veteran's acute nasal congestion in 1970, medically attributed to pneumonia, did not cause his obstructive sleep apnea. Even with attention to the contention, highlighted in Joint Motion I, that the Veteran "reported symptoms of significant fatigue in 2001," there is no indication of the presence of sleep apnea until approximately 30 years after the Veteran's separation from service and his treatment of acute pneumonia in 1970. Joint Motion I expresses concern that a VA medical opinion should not rely upon the 2006 date of diagnosis of sleep apnea without accounting for October 2001 evidence of significant fatigue (and referrals for sleep evaluation in 2002). Unlike the August 2020 VA medical opinion, the December 2025 addendum VA medical opinion does not rely upon citation of a 2006 date of earliest diagnosis in its reasoning. The December 2025 addendum VA medical opinion does not rely upon any specific date of onset of sleep apnea in its reasoning. Rather, the December 2025 addendum VA medical opinion's analysis stands on the medical reasoning that the facts for the Veteran's documented in-service (and proximately post-service) medical history present no valid basis for finding that obstructive sleep apnea was caused or had onset during his active duty service. Furthermore, while the December 2025 addendum VA medical opinion acknowledged that congestion symptoms may in some cases worsen existing sleep apnea, none of the evidence (including the October 2001 evidence of the Veteran's significant fatigue or the 1970 evidence of fatigue attributed to pneumonia) indicate that the Veteran had obstructive sleep apnea that pre-existed his active duty service or his instance on pneumonia in 1970. The facts of this case do not raise further questions regarding any hypothetical pre-existing obstructive sleep apnea being worsened by the Veteran's service. The Board finds that the December 2025 VA medical opinion is competent and probative evidence adequately informed by the record, citing medical principles, and supported by clear and persuasive explanations of rationale. The Board finds that the December 2025 VA medical opinion specifically addresses the 1970 evidence to which Joint Motion II directed special attention. The December 2025 VA medical opinion does not rely upon any assertion that there is no evidence of sleep apnea prior to 2006, thus avoiding the concern of interest in Joint Motion I. As there is no contrary medical evidence of record, the Board finds that the November/December 2025 VA medical opinion is persuasive evidence against the Veteran's claim of entitlement to service connection for obstructive sleep apnea on a direct basis. The Sergeant First Class Heath Robinson Honoring our Promise to Address Comprehensive Toxics Act of 2022 (PACT Act) provides that, when a veteran submits a claim for compensation with evidence of a disability and evidence of a toxic exposure risk activity (TERA) during active military service, and such evidence is not sufficient to establish service connection for the disability, VA shall provide the veteran with a medical examination under 38 U.S.C. § 5103A(d) and obtain a medical opinion as to whether it is at least as likely as not that there is a nexus between the disability and the TERA. The PACT Act further provides that, when providing a medical opinion under this provision, the health care provider shall consider the total potential exposure through all applicable military deployments of the veteran and the synergistic, combined effect of all TERAs of the veteran. The Board has reviewed the Veteran's service records with attention to identifying all TERAs associated with his service experience. The Board finds that the Veteran's service featured the TERA of exposure to tactical herbicide agents during his service in the Republic of Vietnam. The May 2023 VA examination report includes a distinct medical opinion addressing the Veteran's exposure to tactical herbicide agents during service. This portion of the May 2023 VA medical opinion is not the subject of the concerns discussed in Joint Motion II. The May 2023 VA medical opinion concludes that the Veteran's obstructive sleep apnea "is less likely than not (likelihood is less than approximately balanced or nearly equal) caused by the indicated toxic exposure risk activity...." The VA examiner explained the analytical rationale: "Thirty six years after discharge he was diagnosed with... (OSA)... due to passive collapse of the oral or nasal pharynx during inspiration while asleep. There are multiple anatomical abnormalities which may cause or contribute to this airway obstruction... but none are associated with exposure to herbicides specifically." The VA examiner cites multiple sources of medical authority in support of this analysis. The VA examiner then states: "Due to the lack of any pathophysiological relationship between this chemical and OSA, it is less likely as not that the Veteran's Obstructive Sleep Apnea was caused by the toxic exposure to Agent Orange." With regard to this opinion specifically addressing a TERA theory of entitlement, the Board finds that the May 2023 VA medical opinion is competent and probative evidence adequately informed by the record, citing medical principles, and supported by clear and persuasive explanations of rationale. As there is no contrary medical evidence of record, the Board finds that this May 2023 VA medical opinion is persuasive evidence against finding entitlement to service connection for obstructive sleep apnea on the basis of toxic exposures. While the Veteran believes his sleep apnea is proximately due to or the result of his military service, he has not been shown to be competent to provide a nexus opinion regarding this issue. The issue is medically complex, as it falls outside the realm of common knowledge of a layperson. Therefore, it is outside the competence of the Veteran in this case because the record does not show that he has the skills or medical training to make such a determination. Jandreau v. Nicholson, 492 F.3d 1372, 1377 n.4 (Fed. Cir. 2007); see also Kahana v. Shinseki, 24. Vet. App. 428 (2011). Consequently, on the matter of entitlement to service connection for obstructive sleep apnea, the Board finds more probative weight in the November/December 2025 VA medical opinion and the May 2023 VA medical opinion (to the extent of addressing the TERA theory), which are adequate competent evidence probatively informing the Board's review of these matters. For the foregoing reasons, the Board finds that the evidence weighs persuasively against finding that service connection is warranted on any basis for sleep apnea. The Board has considered the doctrine of reasonable doubt but finds that the record does not provide an approximate balance of negative and positive evidence on the merits. The evidence does not establish the existence of a nexus. This decision is in no way meant to diminish the Veteran's honorable service to our country; ? however, service connection must be denied. Gilbert v. Derwinski, 1 Vet. App. 49, 57-58 (1990); 38 U.S.C. § 5107(b); 38 C.F.R. § 3.102. M. C. GRAHAM Veterans Law Judge Board of Veterans' Appeals Attorney for the Board Barone, Alexander The Board's decision in this case is binding only with respect to the instant matter decided. This decision is not precedential and does not establish VA policies or interpretations of general applicability. 38 C.F.R. § 20.1303.