Hemodynamic study of negative pressure ventilation using diaphragm pacing

A negative pressure ventilation (NPV) by unilateral or bilateral diaphragm pacing (DP) was prepared for canine experiments. A shift from positive pressure ventilation (PPV) to NPV resulted in elevation of mean aortic pressure, increase in stroke volume and depression of mean pulmonary arterial pressure. Examination of the interaction between respiratory cycle and cardiac function during PPV, disclosed a reduction of right ventricular stroke volume and elevation of mean aortic and right ventricular end-diastolic pressure at end inspiration, compared to those at end expiration. During NPV with DP, left ventricular stroke volume, heart rate and mean aortic pressure were increased immediately after DP (immediately after inspiration) compared to those at end expiration. The experimental model of DP, in which respiratory condition could be easily altered, was considered to be useful to evaluate the effect of NPV on cardiac function.     

Effects of normobaric and hypobaric hypoxia on ventilation and arterial blood gases in ducks

We measured ventilation (V1) and arterial blood gases in awake Pekin ducks exposed to normoxia at sea level, normobaric hypoxia achieved by lowering FIO2 at normal barometric pressure (NORMO), and hypobaric hypoxia achieved with a low pressure chamber and 21% O2 (HYPO). Average normoxic values were: V1 = 0.46 L . (kg.min)-1, PaO2 = 99.7 Torr, PaCO2 = 30.1 Torr. At PIO2 = 90 Torr, NORMO and HYPO measurements were not significantly different (P greater than 0.05). At PO2 = 46 Torr, NORMO V1 was less than HYPO V1 but blood gases were not significantly different: VI = 1.00 vs 1.45 L . (kg.min)-1; PaO2 = 31.3 vs 33.0 Torr; PaCO2 = 11.5 vs 10.6 Torr. Although both tidal volume (VT) and respiratory frequency (fR) were greater in HYPO, similar blood gases with NORMO and HYPO suggest similar parabronchial ventilation. The results suggest increased physiologic dead space, caused by reduced efficacy of aerodynamic valving, with reduced gas density in hypobaria.     

Effects of emphysema and lung volume reduction surgery on transdiaphragmatic pressure and diaphragm length

STUDY OBJECTIVES: To determine the effect of emphysema and lung volume reduction surgery (LVRS) on diaphragm length (Ldi) and its capacity to generate transdiaphragmatic pressure (Pdi). DESIGN: Prospective clinical trial with a parallel group design. SETTING: Laboratory investigations in normal volunteers recruited by advertisement and in emphysema outpatients being evaluated for elective LVRS. STUDY POPULATION: Thirteen normal subjects and 13 emphysema patients matched for age and sex. Six emphysema patients underwent LVRS. MEASUREMENTS: Ldi and maximal Pdi during static inspiratory efforts (PdiMax) were measured at three different lung volumes (LVs). Pdi during maximal bilateral phrenic nerve twitch stimulation (PdiTw) was measured at functional residual capacity (FRC). All measurements were repeated at 3, 6, and 12 months postoperatively. RESULTS: Ldi, PdiMax, and PdiTw were lower in emphysema patients than in normal subjects at their respective LVs. PdiMax and PdiTw at FRC returned within the normal range after LVRS in emphysema patients. The relationships between PdiMax and LV or Ldi were shifted respectively to higher LV and shorter Ldi in emphysema patients relative to normal subjects, both before and after LVRS. LVRS effected craniad displacement of the diaphragm but no change in rib cage dimensions. Improvements in dyspnea and quality of life after LVRS correlated with changes in LV and Ldi but not with changes in airway caliber. CONCLUSION: Adaptive mechanisms, consistent with sarcomere deletion, tend to restore diaphragm strength in emphysema patients at FRC, which are fully expressed after LVRS. Lung remodeling by LVRS may alter pleural surface pressure distribution, causing a sustained change in chest wall shape.     

Effects of lung volume levels and trapidil on transdiaphragmatic pressure in young healthy subjects

Effects of lung volume levels, and effect of intravenous administration of Trapidil on the maximal force developed by the diaphragm were investigated by the measurement of transdiaphragmatic pressure (Pdi) in 10 healthy young subjects. To evaluate transdiaphragmatic pressure, delta Pdimax was used. delta Pdimax was calculated by the subtraction of the transdiaphragmatic pressure at FRC (Pdi FRC) from the maximal transdiaphragmatic pressure (Pdimax) at each lung-volume level. Regardless of the administration of Trapidil, delta Pdimax was highest at FRC in each subject. When Trapidil was administered, Pdimax increased in cases where absolute Pdimax FRC was initially low. The relation between changes of delta Pdimax at FRC after Trapidil administration and delta Pdimax showed significant linear correlation (r = -0.85, p less than 0.002). These results suggest that FRC is the most adequate lung volume level to produce an effective transdiaphragmatic pressure, and that Trapidil increases the muscle force of the diaphragm in cases where the force is initially low in young healthy subjects.     

Effect of medroxyprogesterone on pulmonary arterial pressure, exhaled nitric oxide, ECG and arterial blood gases

OBJECTIVES: To evaluate the effect of medroxyprogesterone acetate (MPA) therapy on pulmonary arterial pressure (PAP), exhaled nitric oxide (NO), electrocardiogram (ECG), and on arterial blood gases (ABG). DESIGN: A double-blind randomized placebo-controlled cross-over trial. SETTING: University hospital in Turku, Finland. SUBJECTS: Fourteen postmenopausal women with respiratory impairment. INTERVENTIONS: A 2-week placebo and a 2-week MPA period (60 mg day -1) followed by 6-week placebo or MPA washout periods. MAIN OUTCOME MEASURES: The systolic PAP was estimated by Doppler echocardiography. PAP, ECG, NO and ABG were monitored at baseline, after 2-week placebo and MPA periods, and after 3- and 6-week placebo and MPA washout periods. RESULTS: The mean PaCO2 at baseline was 5.4 +/- 0.6 kPa (mean +/- SD). The average decrease of PaCO2 on MPA was -0.8 +/- 0.3 kPa (P < 0.001) and 0.3 +/- 1.0 kPa (P = 0.007) at the 3-week washout. The mean systolic PAP at baseline was 44.3 +/- 14.5 mm Hg. MPA did not change PAP until the 6-week washout, when the average increase of + 6.9 +/- 19.8 mm Hg (P = 0.002) was observed. No changes occurred in PaO2, exhaled NO or the ECG axes. The PR interval was shorter only on MPA (15.9 +/- 27.0 ms, P = 0.020) whereas the QRS duration remained shorter up to 3-week washout (3.9 +/0 5.5 ms, P = 0.008 and 4.0 +/- 14.3 ms, P = 0.032). The systolic and diastolic BP and the heart rate did not change. CONCLUSIONS: Despite prolonged decrease in PaCO2, short-term MPA had no effect on exhaled NO and did not decrease systolic PAP in postmenopausal women with respiratory impairment. MPA shortened the PR interval and the QRS duration, the latter effect being sustained at least up to 3 weeks.     

Effect of transdiaphragmatic pressure partitioning on activation and fatigue of the diaphragm

Fatiguing contractions of the diaphragm during inspiratory resistive loading are accompanied by a predictable rate of decay in the high/low (H/L) frequency ratio of the diaphragmatic EMG (EMG-DI) when the esophageal and gastric pressure (Pes and Pga) components of transdiaphragmatic pressure (Pdi) are equal. However, Pes and Pga do not contribute equally to Pdi under a number of clinical and physiologic conditions. We therefore tested the effect of varying the Pes and Pga contribution to Pdi on the EMG-DI using an esophageal electrode in 5 normal men during fatiguing contractions. Falls in the H/L occurred in all subjects regardless of the relative contribution of Pes and Pga to Pdi at a tension-time index of 0.29 +/- 0.1 (mean +/- SE). However, the time constant of decay of the H/L varied widely among subjects when Pes predominated (173.9 +/- 45.7 s; coefficient of variation, 58.7%) or Pga predominated (78.4 +/- 19.4 s; coefficient of variation, 55.2%), whereas it was consistent among subjects when Pes and Pga were equal (72.3 +/- 3.8 s; coefficient of variation, 11.6%). In addition, a significant relationship was found between the mean integrated activity of the EMG-DI compared with maximum and the time constant of decay of the H/L (r = 0.57, p less than 0.03). We conclude that the differences in the rate of decay of the H/L was at least partly a result of differences in the relative activation of the crural diaphragm at the same Pdi.     

植物雌激素对血压的影响

目的研究大豆饮食中所含的植物雌激素对健康人血压、血脂谱的影响。方法213名健康受试者(男性108人,绝经后女性105人),年龄50-75岁,随机、双盲接受特定大豆蛋白饮食(试验组)或酪蛋白安慰剂(安慰剂组)干预,为期3个月。建立多变量模型以评价治疗效果。结果饮食干预后,仅在试验组受试者尿液中植物雌激素含量增高。试验组血压较安慰剂组下降明显[收缩压(-7.5±1.2)mm Hg比(-3.6±1.1)mm Hg,P<0.01;舒张压(-4.3±0.8)mm Hg比(-1.9±0.7)mm Hg,P<0.05;平均压(-5.5±1.0)mm Hg比(-0.9±1.0)mm Hg,P<0.008]。试验组血脂水平较安慰剂组有显著改变(P<0.001),其中试验组低密度脂蛋白胆固醇/高密度脂蛋白胆固醇比值显著下降[(-0.33±0.10) mmol/L比(0.04±0.10) mmol/L,P<0.05],甘油三酯水平也有显著下降[(-0.20±0.05)mmol/L比(-0.01±0.05)mmol/L,P<0.05],而脂蛋白(a)水平升高(±95%可信区间)[42(17-67)mg/L比4(-22-31)mg/L,P<0.05]。两组中总胆固醇和低密度脂蛋白胆固醇水平均下降,高密度脂蛋白胆固醇水平升高。副作用的发生率两组相似,并且都没有观察到男性激素水平发生改变。结论在正常血压男性和绝经后女性人群中,大豆饮食对血压和血脂水平有改善作用。     

Examination of maximum transdiaphragmatic pressure, diaphragm electromyography in patients with obstructive emphysema]

This paper reported the methods and results of maximum transdiaphragmatic pressure (Pdi max) and diaphragm electromyography (EMGdi) in 16 patients with obstructive emphysema. A correlation analysis showed that Pdimax is negatively related to PaCO2, FRC%, and positively to VC, IC, FVC and MVV closely. Diaphragmatic fatigue was induced by inspiratory resistive loaded breathing with the parameters of 60% Pdimax and 5 minutes lasting. The influential effects and clinical value of diaphragm examination were discussed.     

Cardiovascular function and arterial blood gases during isolated ultrafiltration in healthy man

In order to recognize possible cardiovascular signs of underhydration during isolated ultrafiltration (IUF), we have studied the physiological hemodynamic adaptation to IUF in healthy man both above and below normohydration. In 7 subjects IUF was performed with the subjects in a normohydrated state at the start of IUF. In 8 subjects the IUF was preceded by a 1-hour infusion of Ringer solution equal to 3% of body weight. By invasive techniques, cardiac index (thermodilution), stroke index, heart rate, brachial and pulmonary arterial blood pressures, systemic vascular resistance index, central blood temperature, PaO2 and PaCO2 were measured. Calf vascular resistance was assessed by venous occlusion plethysmography. A recirculation period of 30 min was followed by IUF in both study groups. During IUF with overhydration and normohydration at the start of IUF, cardiac output fell because of a decline in stroke volume and an unchanged heart rate. Blood pressure remained constant because of systemic vascular constriction. PaO2 and PaCO2 remained unchanged. IUF in healthy man is mainly characterized by vascular constriction and an unchanged heart rate. Thus, the cardiovascular adaptation to ultrafiltration was the same whether or not ultrafiltration was performed at overhydration or normohydration at the start of ultrafiltration. Therefore, it is unlikely that monitoring of heart rate or noninvasive recording of blood pressure can predict whether a subject is becoming underhydrated during isolated ultrafiltration. The adaptation to IUF is similar to that observed during the treatment of uremic patients without complications.     

Cardiovascular function and arterial blood gases during sham dialysis in healthy man

Cardiovascular function and alveolar gas exchange were studied in healthy subjects undergoing sham dialysis (SHD)--i.e. the circulation of blood through a cuprophane dialyzer with the dialysate compartment closed to avoid diffusion and convective transport of fluid and solutes. The blood-membrane contact induced complement activation (rise in C3d) and transient leukopenia, as described during clinical hemodialysis. PaO2, PaCO2 and calculated oxygen uptake remained unchanged. Heart rate, cardiac index (thermodilution), systemic vascular resistance index and brachial and pulmonary arterial blood pressures did not change significantly during 150 min of SHD (n = 8). In 12 subjects, in whom more frequent measurements were made during the first 30 min of SHD, pulmonary arterial systolic and diastolic blood pressures decreased significantly while the dialyzer and the tubing set filled with blood, and pulmonary arterial mean blood pressure did not change significantly. Pulmonary capillary wedge pressure fell during the filling phase, but did not change significantly during SHD; pulmonary vascular resistance index remained unchanged. We conclude that in nonuremic subjects sham dialysis with a cuprophane dialyzer does not result in hypoxemia, pulmonary vascular constriction and pulmonary hypertension, in spite of complement activation and marked leukopenia.     

机械通气影响健康志愿者的血流动力学研究

目的观察健康志愿者在不同无创通气模式(CPAP或BiPAP)下,压力变化对血流动力学的影响,探讨正压通气影响血流动力学的机制,为临床实施循环保护通气策略提供依据。方法连续入选30例健康志愿者,每例均先后接受CPAP(压力为0、10、15 cmH 2O)与BiPAP(IPAP 0、15、20 cmH 2O,EPAP 4 cmH 2O)模式并同步监测血流动力学指标。血流动力学监测心率(HR)、心输出量(CO)、心脏动力学指数(CPI)等大循环指标及经皮氧分压(PctO 2)、经皮二氧化碳分压(PctcO 2)等微循环指标。结果在CPAP和BiPAP两种通气模式下随压力的增加,SV、SI变化均无统计学意义(P>0.05),而HR、CI、CO及CPI降低,TPR及TPRI升高,差异有统计学意义(P<0.01);同一模式下改变通气压力PctO 2的变化无统计学意义(P1>0.05),但BiPAP模式下PctO 2较CPAP更高,差异有统计学意义(P2<0.01);两种通气模式下PctcO 2均呈降低趋势(P1<0.01),但BiPAP模式降幅更大,差异有统计学意义(P2<0.01)。结论CPAP和BiPAP均能引起健康志愿者血流动力学改变,心率、心输出量及心肌收缩力指数下降,微循环灌注增加,其中BiPAP对提高组织氧及降低组织二氧化碳的效果更明显。     

The effect of Qat chewing on blood pressure and heart rate in healthy volunteers

The leaves of the Qat plant (Catha edulis Forsk., Celastraceae) which contain amphetamine like compounds are widely chewed in Yemen and East Africa for their pleasurable stimulant properties. There are also a number of unwanted side-effects and this paper studies the effect on heart rate and blood pressure in 80 healthy volunteers. During a 3-h period of chewing fresh Qat leaves there was a significant and progressive rise in systolic and diastolic blood pressure and heart rate, and levels had not returned to baseline 1 h after chewing had ceased. Further studies are needed on possible cardiovascular morbidity associated with regular Qat chewing.     

Effects of bell versus diaphragm on indirect blood pressure measurement

The purpose of this study was to determine the effects of using the bell versus the diaphragm of the stethoscope on indirect blood pressure (BP) measurement. The design was experimental. Data were collected from 56 subjects randomly selected from 255 young women. Systolic (S1), fourth phase diastolic (D4), and fifth phase diastolic (D5) values were the dependent variables. Three research hypotheses were tested. Data were analyzed by using a one-tailed t test for dependent means. Hypotheses 1 and 2 predicted that use of the bell would result in higher S1 and D4 readings, respectively, than use of the diaphragm. Hypothesis 1 was supported whereas hypothesis 2 was not. Hypothesis 3, which stated that using the bell would produce a lower D5 reading than using the diaphragm, was supported. Implications of these findings as well as suggestions for future research are discussed.     

Effect of heparin on arterial blood gases

To evaluate changes in arterial blood gas samples caused by the addition of liquid heparin, 50 patients had three simultaneous blood samples drawn, each with one of three amounts of heparin. The liquid heparin decreased statistically the PCO2, PO2, HCO3, and base excess, while the pH remained unchanged. By using a 2-cc blood sample with a 5-cc glass syringe and a 11/2-inch, 18-gauge needle to draw the heparin solution up to the 2-cc mark, and then completely evacuating it, we found that 0.025 cc of solution remained to coat the syringe. Although this remaining solution would cause a 1.25% error in the blood gas results, the error would be acceptable because it is generally less than the standard deviation of the laboratory results. Excess liquid heparin statistically exaggerated or produced false results consistent with a metabolic acidosis with respiratory compensation. We recommend that the complete evacuation of liquid heparin from the sampling syringe be included when performing an arterial blood gas analysis.