No abstract

Background-A novel device, the intrathoracic pressure regulator (ITPR), combines an inspiratory impedance threshold device (ITD) with a vacuum source for the generation of controlled Ϫ10 mm Hg vacuum in the trachea during cardiopulmonary resuscitation (CPR) while allowing positive pressure ventilation. Compared with standard (STD) CPR, ITPR-CPR will enhance venous return, systemic arterial pressure, and vital organ perfusion in both porcine models of ventricular fibrillation and hypovolemic cardiac arrest. Methods and Results-In protocol 1, 20 pigs (weight, 30Ϯ0.5 kg) were randomized to STD-CPR or ITPR-CPR. After 8 minutes of untreated ventricular fibrillation, CPR was performed for 6 minutes at 100 compressions per minute and positive pressure ventilation (100% O 2 ) with a compression-to-ventilation ratio of 15:2. In protocol 2, 6 animals were bled 50% of their blood volume. After 4 minutes of untreated ventricular fibrillation, interventions were performed for 2 minutes with STD-CPR and 2 minutes of ITPR-CPR. This sequence was repeated. In protocol 3, 6 animals after 8 minutes of untreated VF were treated with ITPR-CPR for 15 minutes, and arterial and venous blood gases were collected at baseline and minutes 5, 10, and 15 of CPR. A newer, leak-proof ITPR device was used. Aortic, right atrial, endotracheal pressure, intracranial pressure, and end-tidal CO 2 values were measured (mm Hg); common carotid arterial flow also was measured (mL/min). Coronary perfusion pressure (diastolic; aortic minus right atrial pressure) and cerebral perfusion pressure (mean arterial minus mean intracranial pressure) were calculated. Unpaired Student t test and Friedman's repeated-measures ANOVA of ranks were used in protocols 1 and 3. A 2-tailed Wilcoxon signed-rank test was used for analysis in protocol 2. Fischer's exact test was used for survival. Significance was set at PϽ0.05. Vital organ perfusion pressures and end-tidal CO 2 were significantly improved with ITPR-CPR in both protocols. In protocol 1, 1-hour survival was 100% with ITPR-CPR and 10% with STD-CPR (Pϭ0.001). Arterial blood pH was significantly lower and PaCO 2 was significantly higher with ITPR-CPR in protocol 1. Arterial oxygen saturation was 100% throughout the study in both protocols. PaCO 2 and PaO 2 remained stable, but metabolic acidosis progressed, as expected, throughout the 15 minutes of CPR in protocol 3. Conclusions-Compared

In the search for more sensitive indicators of airway obstruction Fish et al. (Am. Rev. Respirat. Diseases 109: 700, 1974) have proposed a transit time analysis of the forced expiratory spirogram. In this method the forced vital capacity (FVC) is divided into volumes of air and each volume is assigned a transit time; the nature of the FVC can be described by the transit times' mean, standard deviation, and index of skewness. In a group of 48 healthy nonsmoking subjects between the ages of 9 and 22 yr we found that all three quantities decreased with increasing age. This demonstrates an improvement in the function of the peripheral airways with lung growth. In contrast to the increase in flow rates with lung growth, none of this improved function can be attributed to increased lung volume.