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Biomedical subjects

C S Sassoon

Publications and source records attributed to C S Sassoon.

At least 19 recordsLinked to original sources
PubMed1992

Iatrogenic pneumothorax: etiology and morbidity. Results of a Department of Veterans Affairs Cooperative Study.

The purpose of this study was to delineate the etiological factors for iatrogenic pneumothorax in the era of increased use of invasive procedures and to determine its impact on morbidity. Between 1983 and 1987 the Department of Veterans Affairs conducted a cooperative study at 13 medical centers to assess the utility of the intrapleural instillation of tetracycline for the prevention of recurrent pneumothorax. Since all patients with any type of pneumothorax were screened at each medical center, it was decided to collect data on all the iatrogenic pneumothoraces during that period. During the study period, the number of reported iatrogenic pneumothoraces were 538. Because of incomplete data, 3 iatrogenic pneumothoraces reported from one center were excluded. The leading causes of iatrogenic pneumothorax were transthoracic needle aspiration (128), subclavicular needle stick (119), thoracentesis (106), transbronchial biopsy (54), pleural biopsy (45) and positive pressure ventilation (38). Most patients required treatment for 4-7 days; however, hospitalization was prolonged due to this treatment in only 8% of patients, presumably because of their underlying disease which required long hospitalization. Patients with underlying chronic obstructive pulmonary disease required significantly longer duration of treatment than those without. We conclude that in our patient population, the three leading causes of iatrogenic pneumothorax are transthoracic needle aspiration, subclavicular needle stick and thoracentesis. Hospitalization is prolonged in only a small percentage of the patients who required treatment for the iatrogenic pneumothorax.

Adult↗
PubMed1992

Inspiratory muscle work of breathing during flow-by, demand-flow, and continuous-flow systems in patients with chronic obstructive pulmonary disease.

The effect of flow-by continuous positive airway pressure (CPAP) in comparison with continuous-flow (CF) CPAP on inspiratory muscle work of breathing (WI) in intubated patients is not known. We hypothesized that WI during flow-by CPAP would be comparable with that during CF CPAP. In nine intubated male patients recovering from acute respiratory failure related to chronic obstructive pulmonary disease, we compared the effects of flow-by, demand-flow, and CF CPAP on WI. We also evaluated the extent to which the addition of 5 cm H2O of pressure support to demand-flow CPAP (DF-PS5) decreases WI. At CPAP levels of zero and 8 cm H2O, flow-by, demand-flow, DF-PS5 were applied in random order followed by CF CPAP for 15 min each. WI (expressed as Joules per liter and Joules per minute), maximal airway pressure drop during inspiration (delta Paw), total lung resistance (RL), lung compliance (CL), and ventilatory variables were measured. At CPAP of zero cm H2O, WI with flow-by was comparable with CF CPAP, and significantly less than with demand-flow CPAP. At both CPAP of zero and 8 cm H2O, the addition of 5 cm H2O PS to demand-flow CPAP reduced WI significantly to a level comparable with that of flow-by CPAP. At both CPAP levels, delta Paw was the largest, with demand-flow CPAP. RL and CL were not significantly different between the different CPAP systems. We conclude that WI with flow-by CPAP is comparable with that with CF CPAP, and significantly less than with demand-flow CPAP.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Effects of smoked marijuana of varying potency on ventilatory drive and metabolic rate.

Ventilatory responses to hypercapnia in experienced marijuana smokers have previously been shown to decrease, increase, or not change acutely after marijuana. In one study, minute ventilation (VE) and O2 consumption (VO2) increased but hypoxic ventilatory response did not change after smoking marijuana. We further investigated the effects of marijuana of increasing potency (0, 13, and 20 mg THC) on ventilatory and mouth occlusion pressure (P0.1) responses to hypercapnia and hypoxia in 11 young, healthy men who smoked marijuana regularly but refrained from any smoked substance, alcohol, caffeine, or other drugs for greater than or equal to 12 h before study. Ventilatory and P0.1 responses to hypoxia and hypercapnia were measured on 3 separate days before and 5 and 35 min (hypoxia) and 15 and 45 min (hypercapnia) after smoking. In a companion 3-day study, 12 young male habitual marijuana smokers underwent measurements of VE, VO2, and CO2 production (VCO2) before and 5 to 135 min after smoking marijuana containing 0, 15, or 27 mg THC. None of the active marijuana preparations caused significant changes in ventilatory or P0.1 responses to either hypercapnia or hypoxia or in resting VE, VO2 or VCO2. We conclude that smoking marijuana (13 to 27 mg THC) has no acute effect on central or peripheral ventilatory drive or metabolic rate in habitual marijuana smokers. These conclusions cannot be applied to infrequent users of marijuana without further study.

Adult↗
PubMed1991

Cardiac output from carbon dioxide production and arterial and venous oximetry.

OBJECTIVE: To determine cardiac output from measurements of CO2 production (VCO2), and arterial (SaO2) and mixed venous (SvO2) oxygen saturations, using a modified Fick equation, in which cardiac output = VCO2/[k (SaO2 - SvO2)], where k represents a constant. DESIGN: A metabolic measurement cart was used to measure VCO2 and oxygen consumption (VO2) at 3-min intervals. SaO2 and SvO2 were measured via a pulse oximeter and a fiberoptic right heart catheter, respectively. The initial value of k for each study was determined from initial simultaneous measurements of thermodilution cardiac output, VCO2, SaO2, and SvO2 via the equation k = VCO2/[cardiac output (SaO2 - SvO2)]. The value of k was assumed to remain constant for the entire study period. Thereafter, cardiac outputs calculated from k and the measurements of VCO2, SaO2, and SvO2 were compared with the simultaneously obtained cardiac outputs determined by thermodilution. Similarly, cardiac outputs calculated from the traditional oxygen Fick equation, where cardiac output = VO2/[13.4 x hemoglobin (SaO2 - SvO2)], were compared with the simultaneously acquired cardiac outputs determined by thermodilution. SETTING: Surgical ICU in a Veterans Affairs Medical Center. PATIENTS: Seven postoperative patients, mechanically ventilated using the intermittent mandatory ventilation mode, were studied over a mean period of 4 hrs. RESULTS: Cardiac output (obtained from VCO2 and oximetry saturations) was closely related to thermodilution cardiac output: with linear regression showing r2 = .96 and standard error of the estimate = 0.59 L/min, n = 21; and, with bias and precision = 0.17 and 0.68 L/min, respectively. The traditional oxygen Fick cardiac output was also closely related to the thermodilution cardiac output (r2 = .81, standard error of the estimate = 1.46 L/min, n = 22; bias and precision = 0.31 and 1.46 L/min, respectively). CONCLUSION: The proposed method for calculating cardiac outputs solely from VCO2 and oximetry saturations yields results that correspond closely to thermodilution determined cardiac outputs. The method is simple and avoids the difficulties in the Fick method associated with accurate VO2 measurement. This approach may be suitable for continuous cardiac output monitoring in critically ill patients.

Aged↗
PubMed1991

Pressure-time product during continuous positive airway pressure, pressure support ventilation, and T-piece during weaning from mechanical ventilation.

The objective of this study was to compare the effects of continuous positive airway pressure (CPAP), pressure support ventilation (PS), and T-piece on the pressure-time product (PTP) during weaning from mechanical ventilation. The PTP is an estimate of the metabolic work or oxygen consumption of the respiratory muscles. We studied 10 intubated patients recovering from acute respiratory failure of various etiologies. A modified continuous flow (flow-by) CPAP of 0 and 5 cm H2O (CPAP-0 and CPAP-5, respectively), PS of 5 cm H2O (PS-5), and T-piece were applied in random order for 30 min each. In the last 5 min of the 30-min periods, we measured the esophageal pressure and transdiaphragmatic pressure-time products--PTP(es) and PTP(di), cm H2O.s/min, respectively-multiplied by respiratory frequency. Breathing pattern, total lung resistance (RL), quasi-static lung compliance (CL), intrinsic positive end-expiratory pressure (PEEPi), end-expiratory transpulmonary pressure (Ptpexp), arterial blood gases, blood pressure, and heart rate were also measured. In comparison to T-piece, CPAP-5 decreased PTP(es) 40% (p less than 0.01) and PTP(di) 43% (p less than 0.02), whereas PS-5 decreased PTP(es) 34% (p less than 0.01) and PTP(di) 38% (p less than 0.05). The decrease in PTP(es) with CPAP-5 was associated with a significant reduction in RL, and to a less extent in PEEPi relative to airway pressure. The contribution of the decrease in PEEPi to the reduction in PTP(es) amounted to 36%. With PS-5, respiratory system mechanics and PEEPi were not significantly different compared with T-piece. With CPAP-0, PTP tended to be lower than with T-piece.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Intrapleural tetracycline for the prevention of recurrent spontaneous pneumothorax. Results of a Department of Veterans Affairs cooperative study.

This prospective, multicenter, randomized, "unblinded," controlled clinical trial was designed to determine if the intrapleural instillation of 1500 mg of tetracycline hydrochloride would be effective in diminishing the ipsilateral rate of recurrence for spontaneous pneumothorax. During the 4-year enrollment period, 113 patients were assigned to the tetracycline group; 116 patients were assigned to the control group. During the 5-year study period, the recurrence rate in the tetracycline group (25%) was significantly less than that in the control group (41%). Use of tetracycline seemed to reduce the recurrence rates for patients with either primary or secondary spontaneous pneumothorax and for patients with either an initial or a recurrent pneumothorax. We conclude that the intrapleural administration of tetracycline in patients with spontaneous pneumothorax significantly reduces the rate of ipsilateral recurrence but is associated with intense chest pain. Intrapleural tetracycline therapy is indicated for patients with a spontaneous pneumothorax who are hospitalized and are treated with tube thoracostomy.

Adult↗
PubMed1990

Progress in the development of a fluorescent intravascular blood gas system in man.

In vitro and in vivo animal studies have shown accurate measurements of arterial blood pH (pHa), carbon dioxide tension (PaCO2), and oxygen tension (PaO2) with small intravascular fluorescent probes. Initial human clinical studies showed unexplained intermittent large drops in sensor oxygen tension (PiO2). Normal volunteers were studied to elucidate this problem. In the first part of this study, the probe and cannula were manipulated and the probe configuration and its position within the cannula were varied. The decreases in PiO2 were judged to be primarily due to the sensor touching the arterial wall. Retraction of the sensor tip within the cannula eliminated the problem. In the second part of this study, the accuracy of the retracted probe was evaluated in 4 subjects who breathed varying fractions of inspired oxygen and carbon dioxide. The arterial ranges achieved were 7.20 to 7.59 for pH, 22 to 70 mm Hg for PaCO2, and 46 to 633 mm Hg for PaO2. Linear regression of 48 paired sensor (i) versus arterial values showed pHi = 0.896 pHa + 0.773 (r = 0.98, SEE = 0.017); PiCO2 = 1.05 PaCO2 - 1.33 (r = 0.98, SEE = 2.4 mm Hg); and PiO2 = 1.09 PaO2 - 20.6 (r = 0.99, SEE = 21.2 mm Hg). Bias (defined as the mean differences between sensor and arterial values) and precision (SD of differences) were, respectively, -0.003 and 0.02 for pHi, 0.77 and 2.44 mm Hg for PiCO2, and -2.9 and 25.4 mm Hg for PiO2. The mean in vivo 90% response times for step changes in inspired gas were 2.64, 3.88, and 2.60 minutes, respectively, for pHi, PiCO2, and PiO2.

Blood Gas Monitoring, Transcutaneous↗
PubMed1990

Maximum inspiratory muscle endurance capacity during resistive loading in chronic obstructive pulmonary disease.

In 10 patients with stable severe chronic obstructive pulmonary disease (COPD) we evaluated the relationship between the degree of airway obstruction and hyperinflation, and the maximum inspiratory muscle endurance capacity during added inspiratory resistive loading. We measured the ratio of forced expiratory volume in 1 s to forced vital capacity (FEV1/FVC) and airway resistance (Raw) as indices of airway obstruction, and the ratio of functional residual capacity to total lung capacity (FRC/TLC) as an index of hyperinflation. The mean resting transdiaphragmatic pressure to its maximum (Pdi/Pdimax), the tension time index of the diaphragm, and the maximum transdiaphragmatic pressure (Pdimax) were also determined. Following 15 min of resting breathing, the patients breathed through added inspiratory resistances which were progressively increased every 3 min until exhaustion. Maximum endurance capacity (ECmax) was defined as the product of the esophageal pressure - time integral and frequency at the maximum load sustainable for 3 min. ECmax correlated significantly with Raw (r = -0.67, p less than 0.04). The addition of FRC/TLC to the analysis resulted in a significant increase in the correlation coefficient (r = 0.86, p less than 0.01). ECmax did not correlate with FEV1/FVC. Both resting Pdi/Pdimax and Pdimax independently influenced ECmax. In addition, Pdimax correlated significantly with FRC/TLC, and resting Pdi/Pdimax with Raw. We conclude that in stable patients with severe COPD, both airway obstruction and hyperinflation affect maximum inspiratory muscle endurance capacity during inspiratory resistive loading.

Aged↗
PubMed1990

Respiratory mechanics in anesthetized young patients with kyphoscoliosis. Immediate and delayed effects of corrective spinal surgery.

To our knowledge, the effects of corrective spinal surgery on total respiratory mechanics and its components in anesthetized patients with kyphoscoliosis have not been previously reported in detail. We studied 13 patients with kyposcoliosis; their mean (+/- SD) age was 24.7 +/- 2.1 years; eight underwent anterior and posterior spinal fusions (AF and PF, respectively) two weeks apart (group A), four underwent PF alone (group B), and one had a three-stage procedure. Mean total respiratory elastance (Ers), static and dynamic lung elastance (Est,L and Edyn,L, respectively), chest wall elastance (Ew), and lung resistance (RL) were derived according to previously described methodology. In group A, Ers and Ew increased by 39 percent and 58 percent, respectively, following AF and by 20 percent and 129 percent following PF, while Est,L and Edyn,L did not change or declined following PF. Lung resistance increased 19 percent and 41 percent by the end of AF and PF, respectively, in group A. In group B, Ew more than doubled, resulting in a 39 percent increase in Ers. Increases in Ers, Ew, and respiratory flow resistance observed at the time of spinal corrective surgery for kyphoscoliosis may result from rib cage trauma and changes in airway caliber related to microatelectasis and uneven distribution of mechanical properties within the lungs. Spinal correction results in immediate and short-term deterioration of respiratory mechanics measured under anesthesia.

Adolescent↗
PubMed1990

Ventilator modes: old and new.

CPPV is an accepted standard of treatment in patients with acute respiratory failure. Because of rapid technologic advancements, new modes of ventilation have been developed. Unfortunately, this occurs at a time when there are still many controversies about the relative benefits and modes of action of CPPV. Before the proliferation of use of these newer modes in the intensive care units, documentation of the beneficial effects and safety of these modalities under controlled condition is of utmost importance. Although some of the "new" ventilatory modes (PSV, PAV) improve patient comfort and synchrony, and PAV has the potential to replace CPPV, the superiority of the "new" ventilatory modes over that of CPPV remains to be established, particularly in the area of patient survival, morbidity, and cost.

High-Frequency Ventilation↗
PubMed1989

Inspiratory work of breathing on flow-by and demand-flow continuous positive airway pressure.

Continuous positive airway pressure (CPAP) breathing can be delivered using the demand-flow (DF) or continuous-flow (CF) system. A modified CF system, the flow-by (FB) system, operates with preset base-flow (BF) values between 5 and 20 L/min. The DF depends on changes in pressure for opening the pneumatic valve of the system (pressure sensitivity). In contrast, the FB depends on changes in flow (flow sensitivity). In six healthy male subjects, we determined the mechanical inspiratory work of breathing (WI, J/L) and the inspiratory work rate (J/min) on the DF and the FB systems at a BF of 5 and 20 L/min, at CPAP levels of 0, 5, and 10 cm H2O. In comparison to DF, on the FB system both WI and inspiratory work rate were significantly less at a CPAP of 10 cm H2O (p less than .01). This was most likely due to the smaller drop in airway pressure at the onset of inspiration with the FB system. Varying the BF values in the FB system had no effect on WI or inspiratory work rate.

Adult↗
PubMed1989

Respiratory elastic load compensation in anesthetized patients with kyphoscoliosis.

To evaluate the effects of abnormal respiratory mechanics and neuromuscular drive on the various components of elastic load compensation, we studied 16 anesthetized patients with kyphoscoliosis whose mean passive and active respiratory elastance (Ers and E'rs, respectively), active respiratory resistance, and peak inspiratory occlusion pressure were, respectively, 89, 84, 100, and 37% greater and inspiratory duration (TI) 13% less than corresponding values in 13 anesthetized controls. Ers comprised approximately 66% of effective elastance (E*rs) in both groups. E'rs, reflecting the role of the force-length properties of the active inspiratory muscles in increasing the internal impedance, comprised 83.8 and 86.1% of E*rs in the kyphoscoliosis patients and controls, respectively (P less than 0.001). This demonstrates the influence of increased intrinsic elastance and resistance and decreased TI on tidal volume defense in kyphoscoliosis patients in the absence of vagal modulation. In some patients the difference between Ers and E*rs was substantial, despite an unchanged or even shortened TI, suggesting that the Hering-Breuer reflex may affect stability through ways other than altering TI (e.g., via graded volume-dependent "terminal inhibition"). Characteristics of elastic load compensation in anesthetized kyphoscoliosis patients are similar to those of anesthetized normal subjects.

Adaptation, Physiological↗
PubMed1989

Effect of radiation therapy on bronchial obstruction due to bronchogenic carcinoma.

We evaluated the effect of radiation therapy in 57 patients with obstruction of a large bronchus with NSCC. Response with aeration of the atelectatic lung was seen in 12 patients (21 percent). Three patients (5 percent) showed partial response with persistent partial atelectasis, and nine patients (16 percent) showed good response with complete aeration of the atelectatic lung. In these patients the response appeared to be related to the dose of radiation. All of the patients who responded received more than 50 Gy. The difference in the response rate related to the dose of radiation was statistically significant (p less than 0.05). The rates were similar with all histologic types of NSCC. Regardless of the clinical response observed, bronchoscopy performed two to four months after completion of radiation therapy in 14 patients revealed persistent endobronchial tumor. There was no significant relationship between the persistence of endobronchial tumor, the dose of radiation therapy, and the tumor's histologic type. Of the 12 patients with radiographic improvement in atelectasis, fibrotic changes developed in four (33 percent) patients and pneumonitis in two (17 percent). Progression of disease with distant metastases occurred in 58 percent (seven) of the 12 patients who showed a clinical response of their bronchial obstruction. The median time to survival was nearly identical in responders and nonresponders.

Aged↗
PubMed1988

Work of breathing and airway occlusion pressure during assist-mode mechanical ventilation.

We determined the effect of varying ventilator tidal volume (VT) and inspiratory flow (V) on the inspiratory muscle work (WI) during assist-mode mechanical ventilation (AMV) in four healthy subjects. In another four subjects, under constant chemoreceptor input, we determined the responses of neuromuscular output as assessed by the mouth occlusion pressure (P0.1) to alteration in WI. During AMV, the inspiratory external work of breathing is partitioned between WI and ventilator work. With a constant ventilator trigger sensitivity, we calculated WI (joules/L of volume) as the difference between the area subtended by the airway pressure-inspiratory volume curves and the ordinate of the assisted breaths subtracted from that of the controlled breaths at ventilator V of 40, 60 and 80 L/min and ventilator VT of 100, 125 and 150 percent spontaneous breathing VT. At all ventilator settings, WI was less than inspiratory muscle work of spontaneous breathing (SB) and was a function of both ventilator VT and V (p less than 0.05), but ventilator V has more effect on WI. Under isocapnia and hyperoxia, we measured P0.1 and WI during AMV at ventilator VT of 125 percent of spontaneous breathing VT and ventilator V of 60, 80 and 100 L/min. End-expiratory lung volume remained constant. P0.1 during AMV was similar to that of the SB. Although WI decreased with increasing ventilator V, P0.1 did not decrease significantly. We conclude that during AMV, both ventilator V and to a less extent ventilator VT determine W. In healthy subjects changes in WI do not affect P0.1.

Airway Resistance↗
PubMed1987

Validation of esophageal balloon technique at different lung volumes and postures.

The esophageal balloon technique for measuring pleural surface pressure (Ppl) has recently been shown to be valid in recumbent positions. Questions remain regarding its validity at lung volumes higher and lower than normally observed in upright and horizontal postures, respectively. We therefore evaluated it further in 10 normal subjects, seated and supine, by measuring the ratio of esophageal to mouth pressure changes (delta Pes/delta Pm) during Mueller, Valsalva, and occlusion test maneuvers at FRC, 20, 40, 60, and 80% VC with the balloon placed 5, 10, and 15 cm above the cardia. In general, delta Pes/delta Pm was highest at the 5-cm level, during Mueller maneuvers and occlusion tests, regardless of posture or lung volume (mean range 1.00-1.08). At 10 and 15 cm, there was a progressive increase in delta Pes/delta Pm with volume (from 0.85 to 1.14). During Valsalva maneuvers, delta Pes/delta Pm also tended to increase with volume while supine (range 0.91-1.04), but was not volume-dependent while seated. Qualitatively, observed delta Pes/delta Pm fit predicted corresponding values (based on lung and upper airway compliances). Quantitatively there were discrepancies probably due to lack of measurement of esophageal elastance and to inhomogeneities in delta Ppl. At every lung volume in both postures, there was at least one esophageal site where delta Pes/delta Pm was within 10% of unity.

Adult↗
PubMed1987

Massive pulmonary embolism complicating streptokinase treatment for deep vein thrombosis.

A fatal massive pulmonary embolus developed in a patient treated with streptokinase for acute deep vein thrombosis. This fatal complication occurred despite a careful selection of the patient and the presence of a lytic state. Embolization of a fragmented thrombus or/and attenuation of the lytic state leading to fresh embolization is/are the possible mechanism(s). Although rare, massive pulmonary embolus must be considered to be a major risk of thrombolytic therapy for deep venous thrombosis.

Humans↗
PubMed1987

Airway occlusion pressure. An important indicator for successful weaning in patients with chronic obstructive pulmonary disease.

The objective of this study was to determine whether airway occlusion pressure (P0.1) is a useful predictor for successful weaning during discontinuation of assisted ventilation (AV) in patients with chronic obstructive pulmonary disease (COPD). We studied 12 patients with COPD receiving AV with maximal inspiratory pressure (MIP) less than or equal to -20 cm H2O and FVC greater than or equal to 10 ml/kg. The P0.1, VT, frequency, mean inspiratory flow rate (VT/TI), inspiratory time to total breath cycle duration (TI/Ttot), and arterial blood gases were determined just prior to weaning, within 5 min after discontinuing AV (Time 0), and at 30, 60, 90, 120, 180, and 240 min. Five of the 12 patients failed to wean, defined as requiring AV within 24 h after discontinuing AV. At Time 0, all patients who subsequently failed to wean had a P0.1 of greater than 6 cm H2O, and those who were successfully weaned had a P0.1 of less than 6 cm H2O (p less than 0.001), although the arterial blood gas determinations were comparable in both groups. Throughout the study period, P0.1 in the patients who failed to wean was persistently higher than in the successfully weaned patients. Despite the high P0.1, VT and VT/TI decreased significantly at the termination of the study compared with those at Time 0 in 3 of the patients who failed to wean. Tachypnea was not useful in predicting failure to wean. The TI/Ttot in the patients who failed to wean was persistently lower than in the successfully weaned patients. We conclude that P0.1 is an important indicator for successful weaning.

Aged↗