Estimation of intrapleural pressure in the newborn

We examined the changes in esophageal (Pes), proximal airway (Paw), and direct intrapleural (Ppl) pressure measurements following end-expiratory airway occlusion in anesthetized spontaneously breathing newborn piglets. Simultaneous occluded pressure measurements were obtained during resting ventilation, inspiratory resistive loaded (IRL) breathing, and bilateral transvenous phrenic nerve stimulation. During spontaneous resting ventilation, occluded Paw/Ppl averaged 104 +/- 4% and occluded Pes/Ppl averaged 89 +/- 3%. Similar values were found for occluded spontaneous breaths with IRL. During phrenic nerve stimulation at end-expiratory lung volume, occluded Paw/Ppl averaged 104 +/- 6% while occluded Pes/Ppl decreased to 70 +/- 22%. We conclude that proximal airway pressure more accurately reflects intrapleural pressure than esophageal pressure with occlusion in newborn swine. During phrenic nerve stimulation, esophageal pressure measures are grossly inaccurate estimates of intrapleural pressure with occlusion.     

The pressure-volume relation and the mechanics of left ventricular contraction

The left ventricle is represented as an elastic thick-walled cylinder contracting symmetrically. The force generated by the active state of the myocardium in the radial direction is represented by body force (force/unit volume) and is included in the mathematical formalism that describes the contraction of the left ventricle. An equation for the P-V relation in the left ventricle is derived and various applications to study cardiac mechanics are discussed. The results obtained tend to demonstrate that the active force generated by the myocardium during an ejecting contraction reaches its maximum value near the end of the systolic phase, when the slope E of the P-V line reaches its maximum value Em, and that it is related to the peak isovolumic pressure.     

Relationship of arterial wedge pressure to closing pressure in the pulmonary circulation

We studied the relationship between the pulmonary artery wedge pressure (Pw) and pulmonary venous pressure (Ppv) at 2 alveolar pressures (PA) in 7 isolated perfused dog lobes. If PA were the critical pressure in the pulmonary circulation, one would expect Pw to equal Ppv for all Ppv greater than PA. Relative to the hilum, the average critical pressure in these lobes was 15.07 +/- 0.40 cmH2O at PA = 5 cmH2O and increased significantly to 17.23 +/- 0.82 cmH2O at PA = 7 cmH2O. Because the critical pressure in fact exceeded PA, Pw was found to be relatively constant and independent of Ppv even when Ppv exceeded PA by 5 cmH2O or more. For example, at PA = 5.13 +/- 0.04 cmH2O and Ppv = 9.64 +/- 0.28, the mean value for Pw was 13.30 +/- 0.59 cmH2O. Pw is equal neither to the average critical pressure nor to PA, but instead lies between these two values. It is determined by the spectrum of closing pressures in the pulmonary circulation, and the time-constants for drainage of beds downstream from the occluded pulmonary arterial branch.     

Effects of left ventricular diastolic pressure on the pressure-flow relation of the coronary circulation during physiological vasodilatation

A study to analyse the effects of left ventricular diastolic pressure on coronary pressure-flow relations during physiological vasodilatation was carried out in 14 anaesthetised dogs. The left circumflex artery was perfused at controlled pressures via an extracorporeal circuit and vasodilatation induced by 15 s occlusion of coronary flow. The relation between end diastolic coronary perfusion pressure and flow at peak hyperaemia was linear above 40 mmHg (group 1, n = 7) and became curvilinear at perfusion pressures below 40 mmHg (group 2, n = 7). At a mean left ventricular end diastolic pressure of 8.6(0.8) mmHg the mean zero flow intercept (Pint) in group 1 was 22.5(2.3) mmHg. Graded increases in left ventricular end diastolic pressure by infusion of blood resulted in a parallel rightward shift of the vasodilated pressure-flow relation (Pint = 1.06 X LVEDP + 13.8 mmHg, r = 0.87). The curvilinear relations at low perfusion pressures in group 2 had lower zero flow intercept pressures (Pint = 4.8(0.7) mmHg at left ventricular end diastolic pressure 6.6(1.5) mmHg). As with group 1, graded increases in left ventricular end diastolic pressure caused a rightward shift of the pressure-flow relation, with a direct relation between left ventricular end diastolic pressure and zero flow intercept (Pint = 0.93 X LVEDP + 3.9 mmHg, r = 0.89). Diastolic coronary pressure-flow relations during physiological vasodilatation are essentially linear at perfusion pressures greater than 40 mmHg but are appreciably curved at lower pressures. Increases in left ventricular end diastolic pressure cause a parallel rightward shift of the linear region of the pressure-flow relation.(ABSTRACT TRUNCATED AT 250 WORDS)     

The relation of blood sodium concentration to blood pressure in the rat

Rises or falls in blood sodium concentration ([Na]) within a physiological range of +/- 15 mmol/l, sustained for 5 h, were produced in the rat by intraperitoneal dialysis with physiological salt solutions containing variable amounts of Na. In general, systolic and diastolic blood pressure rose and fell in direct relation to the alteration in [Na]. Solutions of equivalent osmolarity produced changes in blood pressure that were the inverse of those induced by Na. These effects could not be explained in terms of changes in blood or extracellular fluid volume, and indicated the need for an exploration of the partition of Na and water across the vascular smooth muscle cell.     

Pain relief and respiratory mechanics during continuous intrapleural bupivacaine administration after thoracotomy.

Continuous intrapleural bupivacaine administration was assessed in a randomized double-blind manner with respect to its analgesic effect and its impact on breathing after thoracotomy. The pleural cavity was infused continuously for 48 hours in 24 patients following thoracotomy for pulmonary resection. 12 patients received 10 ml/h of bupivacaine hydrochloride 0.5% solution, and 12 patients 10 ml/h NaCl 0.9% solution. There were no differences in the patients' characteristics, extent of surgery, mode and duration of general anaesthesia. There were no complications related either to the catheter or to bupivacaine. The amount of postoperative opioid, given on request, was used to assess the effect of bupivacaine administration on pain relief. Post-thoracotomy breathing was assessed by measuring the forced vital capacity (VC) prior to and after physiotherapy. The VC values measured 24 h, 36 h and 48 h after the operation were similar in both groups of patients with or without bupivacaine administration (p greater than 0.05). Patients given bupivacaine required significantly less opioid analgesia than those who received NaCl 0.9% at 24 h (p less than 0.001), 36 h (p less than 0.001) and 48 h (p less than 0.01) after the operation. Continuous intrapleural bupivacaine analgesia through a paravertebral catheter positioned in the paravertebral groove is safe and provides efficient pain relief after thoracotomy.     

体外循环对P选择素及血栓调节蛋白影响的研究

目的 探讨体外循环对血小板活化及血管内皮细胞损伤的影响及其相互之间的关系。方法 对７例风湿性心脏病患在体外循环前、中、后５个时点采血。用流式细胞仪检测血小板Ｐ选择的表达率及荧光强度,同时用ＥＬＩＳＡ检测血浆中Ｐ选择素及血栓调节蛋白含量。结果 血小板膜Ｐ选择素的表达率从体外循环中１５ｍｉｎ开始上升,６０ｍｉｎ时达高峰,之后逐渐下降,术后２４ｈ仍高于术前水平,各时点之间的差异具统计学意义（Ｐ〈０．０     

Coronary sinus occlusion pressure and its relation to intracardiac pressure

The hemodynamic components of coronary sinus (CS) occlusion pressure in humans have not been well described. If no other outflow for venous blood were present, then after acute occlusion of the coronary sinus the pressure would increase and equal aortic pressure. However, if thebesian vein drainage between the left ventricle and the coronary veins has an important role in humans, then CS occlusion pressure might reflect left ventricular (LV) pressure through transmitted LV pressure or intramyocardial pressure. To study this relation, 27 patients who underwent routine diagnostic cardiac catheterization were evaluated. Occlusion was accomplished by sudden inflation of a No. 7Fr balloon-tipped catheter placed into the CS. LV end-diastolic pressure and end-diastolic CS occlusion pressure were simultaneously recorded at rest. LV end-diastolic pressure (16.7 +/- 5.6 mm Hg) was not significantly different from end-diastolic CS occlusion pressure (15.9 +/- 5.4 mm Hg). LV end-diastolic and end-diastolic CS occlusion pressures were positively correlated (p less than 0.001) over the entire range of pressures (9 to 27 mm Hg). In contrast, systolic CS occlusion pressure was significantly lower than LV systolic pressure and unrelated to right-sided heart pressures. It is concluded that in humans, end-diastolic CS occlusion pressure closely parallels LV end-diastolic pressure, and measurement of CS occlusion pressure to assess LV end-diastolic pressure may have clinical use. These findings also suggest the existence of hemodynamically important thebesian vessel connections that may have implications for retroperfusion or pressure-controlled intermittent CS occlusion in humans.