Lectures on respiratory physiology Respiration under stress

Respiration under stress Exercise High altitude Diving Space flight

Exercise

Respiratory responses to exercise

Comparison of the increases in blood flow and ventilation

Additional changes with exercise Pulmonary artery, venous and capillary pressures rise Recruitment and distension of capillaries Pulmonary vascular resistance falls Pulmonary diffusing capacity increases Shifts of the O 2 dissociation curve Capillaries open up in exercising muscle Systemic vascular resistance falls

High altitude

Decrease of barometric pressure with altitude

Climber on the Everest Summit

Polycythemia at 4600 m altitude Hemoglobin concentration 19.8 g/dl Arterial PO 2 45 mm Hg O 2 saturation 81% O 2 concentration 22.4 ml/dl

PO 2 cascade at sea level and high altitude

Other features of acclimatization Shifts of the O2 dissociation curve Increased concentration of capillaries in muscle Changes in oxidative enzymes in cells

Uneven hypoxic pulmonary vasconstriction exposes some capillaries to high pressure

Diving

Physiological Stresses with Diving Mechanism of decompression sickness Treatment and prevention of decompression sickness Use of helium-oxygen for breathing Saturation diving Inert gas narcosis CNS toxicity caused by high-pressure oxygen Pulmonary oxygen toxicity Hyperbaric oxygen therapy

Concentration of dissolved O 2 in the blood with hyperbaric therapy Barometric pressure = 3 x 760 mm Hg Alveolar and arterial PO 2 exceed 2000 Solubility of O 2 is ml/dl/mm Hg Dissolved O 2 = 6 ml/dl This exceeds the normal arterial-venous difference for O 2

Space flight

Effects of gravity on the lung

Shuttle Launch

Spacelab in the Bay of the Shuttle

Spacelab under 1 G Conditions

Spacelab during Microgravity

Study of Pulmonary Function in Microgravity Package of 9 tests Duration 31 minutes in microgravity Crew member performs test on himself Data available on ground in real time Comprehensive assessment of pulmonary function

Astronaut with the lung function experiment

Pulmonary function in microgravity I Increased pulmonary capillary blood volume Increased pulmonary diffusing capacity Increased cardiac output and stroke volume More uniform distribution of blood flow and ventilation FRC between upright and supine at 1G Residual volume reduced Changes in the deposition of aerosol

Pulmonary function in microgravity II O 2 uptake and CO 2 output unchanged Alveolar PO 2 and PCO 2 unchanged No significant impairment of lung function during two weeks of microgravity On return from six months on the International Space Station, lung function soon returned to pre-flight conditions