Effect of sildenafil and acclimatization on cerebral oxygenation at altitude

Phosphodiesterase-5 inhibitors decrease hypoxic pulmonary vasoconstriction under hypobaric hypoxia, but are not known to affect cerebral blood flow or oxygenation. The present study was designed to evaluate the effect of sildenafil on cerebral haemodynamics during acute exposure to altitude and after acclimatization. Ten subjects were studied 1 and 3 days after rapid ascent to 3480 m before and for two consecutive hours after taking sildenafil (50 mg). Before acclimatization, HR (heart rate) rose at 1 h (76.3+ − 1.0 beats/min compared with 72.5+ − 1.5 beats/min at baseline; P< 0.05) and had returned to baseline at 2 h (71.3+ − 1.1 beats/min; P> 0.05). Mean BP (blood pres-sure) fell from 96.0+ − 2.0 mmHg at baseline to 91.7+ − 2.5 (P< 0.001) at 1 h and 89.8+ − 1.8 mmHg (P< 0.0001) at 2 h, whereas SaO2 (arterial oxygen saturation) increased from 83.9+ − 0.5 % at baseline to 85.3+ − 0.4 % (P< 0.0001) at 1 h and 85.0+ − 0.5 % (P< 0.01) at 2 h. MCAV [MCA (middle cerebral artery) velocity] and PETCO2 (end-tidal partial pressure of CO2) were unchanged, but rSO2 (regional cerebral oxygen saturation) rose progressively at 1 h (62.7+ − 0.8%; P< 0.05) and 2 h (65.3+ − 0.9%; P< 0.0001) compared with baseline (59.3+ − 1.3%). After 3 days of acclimat-ization, resting rSO2 and RMCA (MCA resistance) increased and oxygen delivery fell. Changes in HR and mean BP after sildenafil were similar to day 1, but SaO2 did not change. However, rSO2 increased [61.7+ − 0.9 % at baseline to 65.0+ − 1.0 % (P< 0.0001) at 1 h and 64.0+ − 0.9 % (P< 0.001) at 2h], despite a reduction in MCAV [65.3+ − 1.8 cm/s at baseline to 61.3+ − 1.5 cm/s (P< 0.01