Acute effects of external negative pressure ventilation in chronic obstructive pulmonary disease compared with normal subjects

This study compares the acute physiological effects of external negative pressure ventilation (ENPV) in normal subjects and patients with chronic obstructive pulmonary disease (COPD). The equipment consisted of an airtight jacket (Pneumosuit) and vacuum pump. Minute ventilation (Ve) was recorded using a light-emitting turbine transducer. Oxygen uptake (VO2) and carbon dioxide output (VCO2) were calculated every 30 s. Measurements were made at rest and during ENPV with pressures of -20 cmH2O and -40 cmH2O. The ventilator rate was fixed at 16.min-1. In 10 normal subjects, Ve increased from 8.6 to 22.9 l.min-1 (p less than 0.01) accompanied by an increase in VCO2 from 0.25 to 0.39 l.min-1 (p less than 0.01). In 10 normocapnic COPD patients (arterial carbon dioxide tension (PaCO2) less than 6.0 kPa) Ve increased from 11.5 to 17.1 l.min-1 (p less than 0.01) whilst in 10 hypercapnic patients (PaCO2 greater than 6.0 kPa) Ve increased from 9.7 to 12.4 l.min-1 (p less than 0.01). A change in VCO2 was not detected in the COPD patients, and VO2 did not change in any group. Arterial blood samples were obtained in eight hypercapnic patients. Baseline mean physiological deadspace ventilation (VD) was calculated to be 4.9 l.min-1 (56% of Ve) whilst Ve was 8.8 l.min-1 in this subgroup. During ENPV, arterial oxygen tension (PaO2) increased from 6.8 to 8.2 kPa (p less than 0.01) whilst PaCO2 decreased from 6.8 to 5.8 kPa (p less than 0.01) suggesting that despite the large physiological deadspace, a significant increase in alveolar ventilation had occurred. In advanced COPD, thoracic compliance falls and limits the ventilatory response to ENPV.(ABSTRACT TRUNCATED AT 250 WORDS)