Topic	Key results	References
Lung volumes	Vital capacity unaltered after an initial reduction	13
	Functional residual capacity intermediate between standing and supine positions
	Residual volume reduced
Forced spirometry	Modest changes possibly consistent with increased lung water	14,15
Cardiac output	Increased initially with subsequent decline	16,17
Diffusing capacity	Sustained increase	16
	Increases in both components (membrane diffusing capacity and pulmonary capillary blood volume)
Heterogeneity of ventilation	Reduced in vital capacity breaths	18,19-22
	Minimal changes in tidal volume breaths
Ventilation heterogeneity in lung periphery	Altered in sustained but not transient zero gravity	23-26
Heterogeneity of perfusion	Reduced but not absent	27
Gas exchange and ventilation–perfusion matching	Largely unchanged in zero gravity	28,29
Control of ventilation	Reduction in hypoxic but not hypercapnic ventilatory responses	30,31
Sleep disordered breathing	Evidence for a reduction in zero gravity	32,33
Heart rate variability	Unaltered respiratory sinus arrhythmia in-flight, reduced post-flight	34
Chest wall mechanics	Increase in abdominal contribution to breathing	33,35
Extravehicular activity	No pulmonary disruption	36
Long duration zero gravity	Minimal sustained changes post-flight	37,38

The reader is referred to the primary articles (cited in the table) and to a more extensive review³⁹ for details of these studies.