Pulmonary capillary reserve and exercise capacity at high altitude in healthy humans

Abstract

PurposeWe determined whether well-acclimatized humans have a reserve to recruit pulmonary capillaries in response to exercise at high altitude.MethodsAt sea level, lung diffusing capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (DmCO), and pulmonary capillary blood volume (Vc) were measured at rest before maximal oxygen consumption () was determined in seven adults. Then, DLCO, DmCO and Vc were measured pre- and post-exhaustive incremental exercise at 5150 m after ~40 days of acclimatization.ResultsImmediately after exercise at high altitude, there was an increase in group mean DmCO (14 ± 10 %, P = 0.040) with no pre- to post-exercise change in group mean DLCO (46.9 ± 5.8 vs. 50.6 ± 9.6 ml/min/mmHg, P = 0.213) or Vc (151 ± 28 vs. 158 ± 37 ml, P = 0.693). There was, however, a ~20 % increase in DLCO from pre- to post-exercise at high altitude (51.2 ± 0.2 vs. 61.1 ± 0.2 ml/min/mmHg) with a concomitant increase in DmCO (123 ± 2 vs. 156 ± 4 ml/min/mmHg) and Vc (157 ± 3 vs. 180 ± 8 ml) in 2 of the 7 participants. There was a significant positive relationship between the decrease in from sea level to high altitude and the change in DLCO and lung diffusing capacity for nitric oxide (DLNO) from rest to end-exercise at high altitude.ConclusionThese data suggest that recruitment of the pulmonary capillaries in response to exercise at high altitude is limited in most well-acclimatized humans but that any such a reserve may be associated with better exercise capacity.

Pulmonary Vascular Reserve and Aerobic Exercise Capacity

“…Interestingly, Taylor et al showed that recruitment of pulmonary capillaries in response to exercise at high altitude is limited and may therefore be a significant source of exercise limitation [78]. This is keeping with previous correlation found between lung diffusing capacity for nitric oxide (DL NO ) and VO 2 max at altitude [7,8,74].…”

Standardisation and application of the single-breath determination of nitric oxide uptake in the lung

“…More importantly, the reaction of NO with Hb solutions is 500-1000 times faster than its reaction with blood from animal [23] or human [24] sources. Therefore, θNO cannot be "infinite", as originally thought [10,12] or more recently claimed [18,19]. Further support for a "finite" θNO value comes from physiological experiments where the red cell was "by-passed", either by adding free Hb (by haemolysis) or a haem-based blood substitute to the membrane oxygenator perfusate, or by exchange transfusion of dogs with chemically stabilised bovine haemoglobin (Oxyglobin TM ).…”

“…[11] yielded strong correlations between DLNO (as a surrogate for DMNO) and DMCO for experimental data at rest and at exercise [35,36,109]. Others (for example [18,62,63,94]) preferred the later formula given by FORSTER [4], but negative or excessively high DMCO values have been observed with its use [19]; thus, some [19,25] favoured the formula given by REEVES and PARK [26] and "best fit" α-ratios (all >2.0) for getting the best agreement for DMCO between , with the corresponding LLN, ULN and z-score (standardised residuals: number of standard deviations above or below the reference value) Report alveolar volume in L BTPS and as TLC % pred NO: nitric oxide; O 2 : oxygen; θCO (NO): specific conductance in the blood for carbon monoxide (NO) in mL·(mL blood·min·mmHg) −1 ; DMCO: alveolar-capillary membrane diffusing capacity for CO; PO 2 : oxygen tension; PAO 2 : alveolar oxygen tension; Hb: haemoglobin; DMNO: alveolarcapillary membrane diffusing capacity for NO; KNO: rate of change of NO from alveolar gas; KCO: rate of change of CO from alveolar gas; LLN: lower limit of normal; ULN: upper limit of normal; BTPS: body temperature and pressure, saturated (760 mmHg, 37°C, 100% humidity); TLC: total lung capacity. # : used in tables 1, 2 and 3 and the supplementary appendices.…”

“…After 2-30 days at altitude (4400-5000 m), DLNO and DLCO (at rest) increases in healthy lowlanders [18,63,64]. But acutely (2-3 days' exposure), the DLNO/DLCO ratio falls (8%), and it returns towards baseline (along with DLNO and DLCO) after a week at altitude [63].…”

“…In clinical studies, the fact that DLNO, unlike DLCO, was relatively independent of changes in the inspired oxygen concentration, and thus alveolar oxygen pressure [15,16] and haematocrit [17], which operate through variations in the θ value for blood, seemed to support the original notion that θNO was "effectively" infinite, and that DLNO is a surrogate for the alveolar membrane diffusing capacity, i.e. DLNO=DMNO=1.97·DLCO; this view is still held by some [18,19]. But the current consensus is that DLNO is weighted, but not dominated, by the membrane gas conductance, while the DLCO is dominated by θCO [20].…”