Abstract
Slow deep breathing improves blood oxygenation (SpO2) and affects hemodynamics in hypoxic patients. We investigated the ventilatory and hemodynamic effects of slow deep breathing in normal subjects at high altitude. We collected data in healthy lowlanders staying either at 4559 m for 2–3 days (Study A; N = 39) or at 5400 m for 12–16 days (Study B; N = 28). Study variables, including SpO2 and systemic and pulmonary arterial pressure, were assessed before, during and after 15 minutes of breathing at 6 breaths/min. At the end of slow breathing, an increase in SpO2 (Study A: from 80.2±7.7% to 89.5±8.2%; Study B: from 81.0±4.2% to 88.6±4.5; both p<0.001) and significant reductions in systemic and pulmonary arterial pressure occurred. This was associated with increased tidal volume and no changes in minute ventilation or pulmonary CO diffusion. Slow deep breathing improves ventilation efficiency for oxygen as shown by blood oxygenation increase, and it reduces systemic and pulmonary blood pressure at high altitude but does not change pulmonary gas diffusion.
Highlights
From the point of view of oxygen gas exchange, human lungs are highly inefficient, as suggested by the 50–60 mmHg PO2 gap between atmosphere and arterial blood observed at sea level
Exposure to HA is associated with pulmonary hypertension and lung fluid accumulation, both of which further contribute to hypoxemia and, in some cases, lead to high altitude pulmonary edema (HAPE) [2,3]
All variables returned to baseline values, with the exception of blood oxygenation (SpO2 and PtO2), which remained somewhat higher after 5 minutes of recovery compared with baseline (Table 1, Figure 2)
Summary
From the point of view of oxygen gas exchange, human lungs are highly inefficient, as suggested by the 50–60 mmHg PO2 gap between atmosphere and arterial blood observed at sea level. Efficiency of ventilation for oxygen may be improved by changing the respiratory pattern in order to optimize the partitioning between alveolar ventilation and airway ventilation, being that the latter useless in terms of gas exchange. This has been reported by Yoga practice [4] or by regular breathing as obtained during regular rosary praying [5]. Slow deep breathing may improve arterial oxygenation by increasing alveolar volume and gas exchange at the alveolar capillary membrane level The latter increases when interstitial lung fluids are increased. The mechanisms behind it, being the former but not the latter associated to an increase of extravascular lung fluids [15,16]
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