Physiologic Correlates of Sleep Quality in Severe Emphysema

Background: Sleep quality is poor in severe emphysema. We hypothesized that in addition to nocturnal oxygen desaturation, the severity of airflow obstruction and degree of thoracic hyperinflation are responsible. Methods: Twenty-five patients (14 males, 64 ± 6 [ ± SD] yrs, BMI 24.7 ± 4.2 kg/m²) with severe emphysema (FEV₁ = 28 ± 8% predicted, TLC = 125 ± 14% predicted) were studied. Measurements included spirometry, lung volumes, arterial blood gas, length of the diaphragm's zone of apposition (LZAP) and a polysomnogram. Results: Total sleep time (TST) was 227 ± 93 minutes with a sleep efficiency (SE) of 56 ± 21%. The mean SaO₂, lowest SaO₂, and% TST with a SaO₂ < 90% were 90 ± 5%, 83 ± 8% and 29 ± 40%, respectively. TST correlated with FEV₁% (r = 0.5, p = 0.02), FVC% (r = 0.4, p = 0.03) and LZAP (r = 0.5, p = 0.01). SE correlated with FEV₁% (r = 0.5, p = 0.02) and LZAP (r = 0.5, p = 0.01), but not with FVC% (r = 0.4, p = 0.07). Additionally, TST and SE correlated negatively with residual volume% (r = -0.4, p = 0.046, and r = -0.4, p = 0.03, respectively). There was no correlation between TST and SE and measures of nocturnal oxygenation. Multiple linear regression was used to predict TST, with 50% (r² = 0.49) explained by a combination of LZAP (27%), mean SaO₂ (23%), and the lowest SaO₂ (< 1%). To predict SE, 44% (r² = 0.43) was explained by a combination of LZAP (29%), mean SaO₂ (14%), and the lowest SaO₂ (1%). Conclusion: Although parameters of respiratory function and mechanics correlate with sleep quality, both nocturnal oxygenation and measurements of respiratory function/mechanics predict sleep quality in severe emphysema.