Variables used to set PEEP in the lung lavage model are poorly related.
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Setting an appropriate positive end-expiratory pressure (PEEP) value is determined by respiratory mechanics, gas exchange and oxygen transport. As these variables may be optimal at different PEEP values, a unique PEEP value may not exist which satisfies both the demands of minimizing mechanical stress and optimizing oxygen transport. In 15 surfactant-deficient piglets, PEEP was increased progressively. Arterial oxygenation and functional residual capacity (FRC) increased, while specific compliance of the respiratory system decreased. Static compliance increased up to a threshold value of PEEP of 8 cm H2O, after which it decreased. This threshold PEEP did not coincide with the lower inflection point of the inspiratory limb of the pressure-volume (PV) loop. Oxygen transport did not correlate with respiratory mechanics or FRC. In the lavage model, the lower inflection point of the PV curve may reflect opening pressure rather than the pressure required to keep the recruited lung open. Recruitment takes place together with a change in the elastic properties of the already open parts of the lung. No single PEEP level is optimal for both oxygen transport and reduction of mechanical stress. (+info)
Cardiorespiratory interactions during periodic breathing in awake chronic heart failure patients.
(58/1040)
We applied spectral techniques to the analysis of cardiorespiratory signals [instantaneous lung volume (ILV), instantaneous tidal volume (ITV), arterial O(2) saturation (Sa(O(2))) at the ear, heart rate (HR), systolic (SAP), and diastolic (DAP) arterial pressure] during nonapneic periodic breathing (PB) in 29 awake chronic heart failure (CHF) patients and estimated the timing relationships between respiratory and slow cardiovascular (<0.04 Hz) oscillations. Our aim was 1) to elucidate major mechanisms involved in cardiorespiratory interactions during PB and 2) to test the hypothesis of a central vasomotor origin of PB. All cardiovascular signals were characterized by a dominant (>/=84% of total power) oscillation at the frequency of PB (mean +/- SE: 0.022 +/- 0.0008 Hz), highly coherent (>/=0.89), and delayed with respect to ITV (ITV-HR, 2.4 +/- 0.72 s; ITV-SAP, 6.7 +/- 0.65 s; ITV-DAP, 3.2 +/- 0.61 s; P < 0.01). Sa(O(2)) was highly coherent with (coherence function = 0.96 +/- 0. 009) and almost opposite in phase to ITV. These findings demonstrate the existence of a generalized cardiorespiratory rhythm led by the ventilatory oscillation and suggest that 1) the cyclic increase in inspiratory drive and cardiopulmonary reflexes and 2) mechanical effects of PB-induced changes in intrathoracic pressure are the more likely sources of the HR and blood pressure oscillations, respectively. The timing relationship between ITV and blood pressure signals excludes the possibility that PB represents the effect of a central vasomotor rhythm. (+info)
Importance of adjusting carbon monoxide diffusing capacity (DLCO) and carbon monoxide transfer coefficient (KCO) for alveolar volume.
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The volume dependence of single breath carbon monoxide diffusing capacity (DLCO) and carbon monoxide transfer coefficient (KCO) was determined in 24 healthy subjects. The change in DLCO [fraction of DLCO measured at total lung capacity (TLC)] to change in alveolar volume [fraction of alveolar volume (VA) at TLC] closely fitted a simple linear regression and matched a theoretical model. As VA decreased, DLCO fell linearly and KCO increased as expected from the relation of DLCO to VA. The equations for adjustment of predicted DLCO and KCO for alveolar volume are: DLCO/DL COtlc = 0.58 + 0.42 VA/VAtlc, KCO/KCOtlc = 0.42 + 0.58/(VA/VAtlc). DLCO and KCO were evaluated in 2313 patients. Subgroups of patients with asthma, emphysema, extrapulmonary lung disease, interstitial lung disease and lung resection were identified. Unadjusted DLCO and KCO percent predicted values showed large differences and much variability, so can be misleading. As expected, KCO and DLCO percent predicted values adjusted for alveolar volume were nearly identical. Subgroups have characteristic patterns of VA and unadjusted and adjusted DLCO and KCO. Changes in DLCO and KCO with alveolar volume are relevant for accurate interpretation of diffusion in patients with low lung volumes. Adjusting predicted DLCO and KCO for alveolar volume provides a better assessment of lung function. (+info)
Airway distensibility in healthy and asthmatic subjects: effect of lung volume history.
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Anatomic dead space (VD) is known to increase with end-inspiratory lung volume (EILV), and the gradient of the relationship has been proposed as an index of airway distensibility (DeltaVD). The aims of this study were to apply a rapid method for measuring DeltaVD and to determine whether it was affected by lung volume history. VD of 16 healthy and 16 mildly asthmatic subjects was measured at a number of known EILVs by using a tidal breathing, CO(2)-washout method. The effect of lung volume history was assessed by using three tidal breathing regimens: 1) three discrete EILVs (low/medium/high; LMH); 2) progressively decreasing EILVs from total lung capacity (TLC; TLC-RV); and 3) progressively increasing EILVs from residual volume (RV; RV-TLC). DeltaVD was lower in the asthmatic group for the LMH (25.3 +/- 2.24 vs. 21.2 +/- 1.66 ml/l, means +/- SE) and TLC-RV (24. 3 +/- 1.69 vs. 18.7 +/- 1.16 ml/l) regimens. There was a trend for a lower DeltaVD in the asthmatic group for the RV-TLC regimen (23.3 +/- 2.19 vs. 18.8 +/- 1.68 ml/l). There was no difference in DeltaVD between groups. In conclusion, mild asthmatic subjects have stiffer airways than normal subjects, and this is not obviously affected by lung volume history. (+info)
Sink or swim: strategies for cost-efficient diving by marine mammals.
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Locomotor activity by diving marine mammals is accomplished while breath-holding and often exceeds predicted aerobic capacities. Video sequences of freely diving seals and whales wearing submersible cameras reveal a behavioral strategy that improves energetic efficiency in these animals. Prolonged gliding (greater than 78% descent duration) occurred during dives exceeding 80 meters in depth. Gliding was attributed to buoyancy changes with lung compression at depth. By modifying locomotor patterns to take advantage of these physical changes, Weddell seals realized a 9.2 to 59.6% reduction in diving energetic costs. This energy-conserving strategy allows marine mammals to increase aerobic dive duration and achieve remarkable depths despite limited oxygen availability when submerged. (+info)
Laparoscopic and laparotomic cholecystectomy: a randomized trial comparing postoperative respiratory function.
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BACKGROUND: The fact that pulmonary complications occur in 20-60% of the patients subjected to abdominal operations clearly indicates that the lungs are the most endangered organ during the postoperative period. OBJECTIVE: The aim of this study was to demonstrate the impact of cholecystectomy on postoperative respiratory disturbances by comparing the laparotomic cholecystectomy with laparoscopic gallbladder removal. PATIENTS AND METHODS: A hundred cholecystectomized patients were included in the prospective randomized clinical trial. Half of the patients were operated on by the laparotomic procedure, whereas the other half underwent laparoscopic cholecystectomy. Spirometric parameters, arterial blood gases, and acid-base balance were determined before the operation, and at 6, 24, 72 and 144 h postoperatively. Abdominal distension was assessed by auscultating intestinal peristaltics, abdominal circumference measurement, and time interval to restitution of defecation. RESULTS: Six hours postoperatively, the values of ventilation parameters decreased on average by 40-50% from the baseline preoperative values in both groups of patients. The group of patients submitted to laparotomic cholecystectomy had significantly lower spirometric values and slower recovery of the ventilation parameters than the laparoscopic cholecystectomy group. Abdominal circumference was significantly greater and the time needed for restitution of peristaltics and defecation was significantly longer in the laparotomic cholecystectomy group compared to the group of laparoscopic cholecystectomy. CONCLUSIONS: Statistically significant impairments including hypoxia, hypocapnia and hyperventilation were observed in the patients submitted to laparotomic cholecystectomy, indicating the presence of objective respiratory risk, especially in elderly patients and patients with obstructive pulmonary diseases or cardiac insufficiency. (+info)
Postoperative respiratory effects of morphine and halothane anesthesia: a study in patients undergoing cardiac surgery.
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Lung volumes, deadspace, ventilation, and ventilatory response to CO2 challenge were studied on the day before and for the first three days after corrective cardiac surgery. Ten patients underwent coronary artery bypass grafting and ten patients had mitral valve prostheses inserted. Half of the patients in each group received halothane as the major anesthetic, and the other half received morphine sulfate (1-2 mg/kg). Mitral valve-replacement patients anesthetized with morphine showed lower CO2 sensitivity on the first postoperative day than those who received halothane. Patients who had coronary artery bypass grafts tended to hyperventilate during the postoperative period, but this did not occur on the first postoperative day in those who received morphine anesthesia. Respiratory rate was always higher postoperatively, most markedly in patients who receivedhalothane for coronary artery bypass grafts. Vital capacity was diminished by 67 per cent in all groups postoperatively. VD/VT tended to increase during the first and second postoperative days and then decrease toward control values on the third postoperative day in all groups except valve-replacement patients who received morphine. Morphine anesthesia may increase the period of mechanical ventilation necessary after cardiac surgery partly as a result of impaired CO2 sensitivity. (+info)
Effects of lung volume on parasternal pressure-generating capacity in dogs.
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Previous studies have suggested that the optimum length for force generation of the parasternal intercostal (PS) muscles is well above functional residual capacity (FRC). We further explored this issue by examining the pressure-generating capacity of the PS muscles as a function of lung volume in anaesthetized dogs. Upper thoracic spinal cord stimulation (SCS) was used to electrically activate the PS muscles. Changes in airway pressure and parasternal resting length (LR) during airway occlusion were monitored over a wide range of lung volumes during SCS. To assess the effects of parasternal contraction alone, SCS was performed following phrenicotomy and section of the external intercostal, levator costae and triangularis sterni muscles. With increasing lung volume, there were progressive decrements in the capacity of the PS muscles to produce changes in airway pressure. The relationship between PS pressure generation and lung volume was similar to a previous comparable assessment of the external intercostal muscles. The PS muscles shortened during passive inflation and also shortened further (by > 20 % of LR) during SCS. Total shortening (passive plus active) increased progressively with increasing lung volume. Our results indicate that the capacity of the PS muscles to produce changes in airway pressure (a) falls progressively with increasing lung volume and (b) is similar to that of the external intercostal muscles. We speculate that the fall in PS pressure-generating capacity is related, in part, to progressive reductions in end-inspiratory length. (+info)