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PubMedDate not supplied

Regulation of the tidal volume and ventilatory responses to CO2 in normal man and in scoliosis.

The variation of the ventilatory response to CO2 and its pattern among normals and in the presence of pulmonary disease is wide. In normal subjects the relationship between the slopes of the ventilatory (delta V/delta PCO2), tidal volume (delta VT/delta PCO2) and the frequency (delta f/delta PCO2) responses and body size, metabolic rate, resting ventilation and pattern, lung volumes or mechanical properties of the respiratory system have only been demonstrated in a few studies. In idiopathic scoliosis there is a positive correlation between the delta V/delta PCO2 and delta VT/delta PCO2 and body size, resting ventilation and tidal volume, lung volumes and compliance of the respiratory system. Although there were significant correlations between the delta V/delta PCO2 and the delta VT/delta PCO2 and th delta f/delta PCO2 the correlation between the delta VT/delta PCO2 and delta f/delta PCO2 was not significant. Correlations between the delta f/delta PCO2 and lung volumes, compliance or body size were also not significant. Therefore variation in the frequency response to CO2 contribute to the variation between individuals of the delta V/delta PCO2 and this variation is unrelated to respiratory mechanics or body size. We conclude that in human studies any examination of possible relationships between ventilatory response to CO2 and body size, lung volumes and mechanics should examine separately the tidal volume and frequency response to CO2. We postulate that the tidal volume response is the most appropriate variable to normalize for lung volumes, e.g., vital capacity (delta VT/VC/delta/ PCO2).

Adult↗

PubMed1993

Tidal volume, lung hyperinflation and arterial oxygenation during general anaesthesia.

Impaired pulmonary oxygen (O2) exchange is common during general anaesthesia but there is no clinical unanimity as to methods of prevention or treatment. We studied 14 patients at risk for pulmonary dysfunction because of increased age, obesity, cigarette smoking, or chronic lung disease. Pulmonary O2 exchange was measured during four conditions of ventilation: awake spontaneous, conventional tidal volume (CVT, 7 ml.kg-1) or high tidal volume (HVT, 12 ml.kg-1) controlled ventilation, and five min after manual hyperinflation (HI) of the lungs. The FIO2 was controlled at 0.5, and FETCO2 was kept constant by adding dead space during HVT. Eight patients were ventilated with N2O/O2 and six with air/O2. Arterial blood gases were used to calculate the (A-a)DO2. In seven patients (A-a)DO2 worsened after induction of anaesthesia, while in seven there was no change or an improvement. Manual HI significantly reduced (A-a)DO2, but changing tidal volume (VT) had no effect. Using a multivariate model to predict O2 exchange, obesity and type of surgery were significantly associated with worsening, while level of VT and inspiratory gas (N2O or N2) were not significant predictors. Thus patient and surgical factors were more important determinants of pulmonary gas exchange during anaesthesia than were tidal volume or inspiratory gas. Manual HI is a simple and effective manoeuvre to improve gas exchange.

Adult↗

PubMed2001

Accuracy and consistency of respiratory inductive plethysmography for overnight tidal volume measurement.

To validate the accuracy and consistency of respiratory inductive plethysmography (RIP) in measuring tidal volume after an overnight sleep, tidal volumes of 18 patients with suspected sleep-disordered breathing and 8 normal volunteers were measured simultaneously with RIP (VTRIP) and with an ultrasonic airflow meter (VTUFM) before and after an unstrained overnight sleep on supine and lateral decubitus. The bias of the VTRIP was expressed as (VTRIP-VTUFM)/ VTUFM.100%, limits of agreement between VTRIP and VTUFM was measured by averaged bias +/- 2 s. Results showed that in normal subjects, the bias of RIP before and after overnight sleep was precise and consistent in both supine (0.7% and -1.6%) and lateral decubitus (3.7% and -0.56%). In these patients, the bias of RIP before and after sleep in supine also remained small (1.9% and 1.7%), but it became larger in lateral decubitus (24.5% and 20.4%) and 11.5% exceeded the limits of agreement observed in the evening. The patients' body mass indices (BMI) were higher than those of normal subjects (median 34.2 vs. 27.8 kg/m2). Pooled data showed that the bias of VTRIP in the morning on lateral decubitus but not on supine was correlated to BMI (Spearman R = 0.32, n = 52, P = 0.02). Thus, we were led to conclude that the accuracy of VTRIP overnight was precise and consistent in normal subjects, but the deviation of VTRIP measured on lateral decubitus in patients especially in those with excessive obesity was greater, thus, the method should not be used for quantitative determination.

Adult↗

PubMed1975

[The effect of the tidal volume on the sinus arrhythmia of the heart].

The sinus arrhythmia of the human heart was investigated in its relation to the tidal volume under resting conditions in the course of the day, in voluntarily changed tidal volume, under atropine medication and during physical work. In resting conditions it was found that nearly 40% of the sinus arrhythmia is of respiratory origin, and that no respiratory influence is demonstrable any longer at sufficient doses of atropine. Under physical load, the sinus arrhythmia is diminished in spite of the enlarged tidal volume. In this case, an additional smoothing influence to the sinus arrhythmia has to be assumed.

Adult↗

PubMed1996

Effect of detergent combined with large tidal volume ventilation on alveolocapillary permeability.

The combined effect of large tidal volume ventilation (LTVV) and detergent-induced surfactant dysfunction on the clearance kinetics of technetium-99m-labelled diethylene triamine pentaacetate was investigated. Four groups of rabbits (n = 6 in each) were studied: (1) controls, (2) detergent, (3) LTVV, and (4) detergent + LTVV. Clearance was measured for 3 h and the kinetics was analysed by fitting mono- and biexponential equations to the clearance curve and was expressed as a half-life (T 1/2). Pulmonary clearance of 99mTc-DTPA was monoexponential in control animals (T 1/2 = 194 min) and in animals ventilated with LTVV (T 1/2 = 43 min, P < 0.01 compared with controls). In contrast, clearance was biexponential after detergent administration with or without LTVV. T 1/2 values of the fast and slow compartments were 5.4 and 80 min, respectively, with the fast fraction comprising 81% of the radioactivity after detergent alone. When detergent was combined with LTVV, clearance was bicompartmental as with detergent alone, with the same size of the fast fraction. However, clearance from each of the slow (P < 0.01) and fast compartments (P < 0.05) increased significantly. Clearance from the slow compartment was thus similar to T 1/2 during LTVV alone. Large tidal volume ventilation induced a faster than normal clearance of a single compartment, whereas detergent induced kinetics that was distinctly bicompartmental. The mechanisms increasing permeability of the alveolocapillary barrier after detergent and during LTVV seem different and may be additive.

Aerosols↗

PubMed1979

Artificial ventilation in children during anaesthesia using a tidal volume ventilator.

Standards for artificial pulmonary ventilation at ventilatory frequencies of 15 and 20 cycles per min, (PETCO2 4 +/- 0.5 kPa), were defined in 16 children with healthy lungs and body weights between 2.6 and 22.6 kg. A tidal volume ventilator and balanced anaesthesia were used during abdominal surgery. At f = 20 cycles/min an approximately direct proportionality existed between tidal volume and body weight (VTpat = 12.3 . kg b.w.--2.1, r = 0.99). The mean value VTpat per kg b.w. was 12.1 +/- 1.4 ml/kg. At f = 15 cycles/min, a linear relationship between tidal volume and kg b.w. was recorded (VTpat = 14.6 . kg b.w. + 16, r = 0.97). The mean value VTpat per kg b.w. was 15.9 +/- 1.5 ml/kg. A significant decrease in total compliance was recorded during the initial part of the surgical procedure. A rectilinear relationship existed between total compliance and kg b.w. (CTOT = 11.2 . kg b.w.--12.5, r = 0.95). The mean value CTOT per kg b.w. was 9.7 +/- 0.54 ml/kPa/kg at f = 20. The endotracheal peak pressure maintained a fairly constant pressure level independent of the initial pressure within the ventilator, the tidal volume and the body weight, a phenomenon explained by the hypothesis that the proportional increase in total lung volume and functional residual capacity in the older children compensated for the higher pressures.

Abdomen↗

PubMed1999

The effect of tidal volumes on the time to wean persons with high tetraplegia from ventilators.

STUDY DESIGN: Retrospective review of patient medical records comparing the outcomes of two groups of individuals with high-level (C3-4) tetraplegia- those with high-volume and those with low-volume mechanical ventilation. OBJECTIVES: To determine if higher volume mechanical ventilation contributes to faster weaning from the ventilator with fewer complications in individuals with ventilator dependent high-level tetraplegia. SETTING: A Model Spinal Injury Center, located in Colorado, USA, which treats patients referred from throughout the Rocky Mountain region as well as other states. METHODS: The medical records of 42 individuals with ventilator dependent C3-4 tetraplegia, admitted consecutively to the Rocky Mountain Regional Spinal Injury System between 1983 and 1993, were reviewed. All had required full-time mechanical ventilation upon admission, but had successfully weaned by discharge. They were divided into two groups that differed with respect to the ventilator tidal volumes used during their treatment and weaning: a large volume group (> 20 mls/kg of body weight) and a smaller volume group (< 20 mls/kg of body weight). RESULTS: Though the two groups were equivalent in neurological level and completeness, muscular function, initial spontaneous vital capacity, the weaning method used (T-piece), and final spontaneous vital capacity, those in the large tidal volume group successfully weaned an average of 21 days faster than the lower tidal volume group (37.6 days vs 58.7 days, P=0.02). They also had significantly less atelectasis (P=0.01) than the lower tidal volume group. CONCLUSION: This research suggests that the use of higher ventilator tidal volumes may speed up the weaning process and lessen respiratory complications. Because of the potential for this to decrease the length and cost of the rehabilitation programs for persons with high-level tetraplegia, further large-scale research is needed to verify these single-center findings.

Adolescent↗

PubMed1978

Dead space and tidal volume of the giraffe compared with some other mammals.

The ventilation, tidal volume and anatomical dead-space were measured in a living giraffe and compared with similar measurements in a camel, red deer, llama and man. The giraffe had a resting tidal volume of about 3.3 litres with a dead-space/tidal-volume ratio of 0.34. The giraffe breathes slowly, apparently because of the unusually small diameter of its trachea relative to its length, compared with known measurement in other mammals.

Animals↗

PubMed2006

Ventilation and perfusion distribution during altered PEEP in the left lung in the left lateral decubitus posture with unchanged tidal volume in dogs.

Previous studies in anesthetized humans positioned in the left lateral decubitus (LLD) posture have shown that unilateral positive end-expiratory pressure (PEEP) to the dependent lung produce a more even ventilation distribution and improves gas exchange. Unilateral PEEP to the dependent lung may offer special advantages during LLD surgery by reducing the alveolar-to-arterial oxygen pressure difference {(A-a)PO2 or venous admixture} in patients with thoracic trauma or unilateral lung injury. We measured the effects of unilateral PEEP on regional distribution of blood flow (Q) and ventilation (V(A)) using fluorescent microspheres in pentobarbital anesthetized and air ventilation dogs in left lateral decubitus posture with synchronous lung inflation. Tidal volume to left and right lung is maintained constant to permit the effect on gas exchange to be examined. The addition of unilateral PEEP to the left lung increased its FRC with no change in left-right blood flow distribution or venous admixture. The overall lung V(A)/Q distribution remained relatively constant with increasing unilateral PEEP. Bilateral PEEP disproportionately increased FRC in the right lung but again produced no significant changes in venous admixture or V(A)/Q distribution. We conclude that the reduced dependent lung blood flow observed without PEEP occurs secondary to a reduction in lung volume. When tidal volume is maintained, unilateral PEEP increases dependent lung volume with little effect of perfusion distribution maintaining gas exchange.

Adaptation, Physiological↗

PubMed1985

Regional tidal volume assessed by gated lung imaging.

We have measured regional lung tidal volumes and functional residual capacities by accumulating and framing iso-volumic images while the patient rebreathes 127Xe. As the lung changes shape during ventilation corrections for changes in geometry were obtained by simultaneous collection of 99Tcm counts from the gated perfusion scan. Regions of interest were made to vary throughout the respiratory cycle so that a region had always the same value of 99Tcm counts. From the corrected 127Xe counts regional tidal volumes (TVr) and functional residual capacities (FRCr) were derived. In patients with established chronic bronchitis and emphysema FRCr were greater and the ratio TVr/FRCr decreased compared with patients with relatively normal static and dynamic lung volumes. Preliminary studies suggest that this ratio was a better discriminator between normal and abnormal regional function than estimates of regional xenon washout. Studies with xenon-133 have contributed to our understanding of the physiology of ventilation but have contributed somewhat less to routine clinical practice. This results in part from the unsatisfactory physical properties of xenon-133. Its relatively low gamma ray energy of 80 keV results in significant self-absorption losses and the activity which may be administered is limited by the radiation dose from the associated beta particles so that relatively poor counting statistics are obtained. With inhaled technetium-99m (99Tcm) microspheres imaging conditions are greatly improved but the distribution of these particles may not equate with the distribution of ventilation particularly if wet particles are used. Moreover, simultaneous microsphere perfusion scans with technetium-99m as a label are impossible. Krypton-81m gas has a suitable energy but the short half-life of the rubidium-81m generator (4.7 h) makes supply difficult and the ultrashort half-life of the krypton-81m gas (13 s) leads to problems in calculating the indices of ventilation. Xenon-127 (127Xe) gas has a more favourable dosimetry profile than xenon-133 because it does not have associated beta particles. Further it has an energy (203 keV) suitable for modern gamma cameras and may be used in the presence of injected 99Tcm microspheres to provide simultaneous ventilation/perfusion imaging. Conventional techniques have assumed that a static image of a dynamic process is adequate. As the lungs move during imaging, some account of this respiratory movement should be made.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Effects of positive end-expiratory pressure on regional distribution of tidal volume and recruitment in adult respiratory distress syndrome.

The distribution of tidal volume (VT) and recruitment was investigated by chest computed tomography (CT) in eight sedated-paralyzed patients with the adult respiratory distress syndrome (ARDS). A CT section was obtained in the supine position at 0, 5, 10, 15, and 20 cm H2O positive end-expiratory pressure (PEEP) and at the corresponding inspiratory plateau pressure (21 +/- 1.8, 26 +/- 1.4, 31 +/- 1.8, 38 +/- 2.1, and 46 +/- 3.2 cm H2O [mean +/- SE]), keeping VT constant. Each CT section was divided along its ventral-dorsal height into 10 equally spaced intervals (levels). Vi(insp) and Vi(exp) were defined as the gas volume for level i (i = 1 to 10) at end-inspiration and at end-expiration, respectively. The following variables were computed at each lung level: (1) distribution of CT section tidal volume (VTct), i.e., the fraction of VT that inflates a given lung level; (2) the plateau-induced and PEEP-induced recruitment, i.e., the amount of lung tissue previously collapsed that inflates at plateau pressure and at PEEP, respectively; (3) the reopening-collapsing tissue, i.e., the amount of lung tissue that regains inflation at plateau pressure and collapses at PEEP. With increasing PEEP from 0 to 20 cm H2O, the VTct distribution decreased significantly (p < 0.01) in the upper levels, did not change in the middle levels, and increased significantly (p < 0.01) in the lower levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1980

Relation between respiratory valve dead space and tidal volume.

We measured the "effective" dead space of five commonly used respiratory valves: Hans Rudolph valve, two-way J valve, triple-J valve, and modified Otis-McKerrow valves without and with vane. The dead space was measured using a technique that mimicked the operation of valves during ordinary laboratory procedures. The valves were ventilated with tidal volumes ranging from 0.35-3.00 liters and at different frequencies. With all valves, there was a marked tendency for "effective" dead space to be tidal volume dependent. The measured dead space approached the water-displacement volume of the common chamber of the valve only at tidal volumes in excess of 2.0 liters. The relation between valve dead space and tidal volume was independent of frequency.

Mathematics↗

PubMed1997

Haemodynamic and catecholamine changes during rapid sevoflurane induction with tidal volume breathing.

PURPOSE: To compare haemodynamic and plasma catecholamine changes with rapid (three minute) inhalational anaesthesia induction with tidal volume breathing of sevoflurane 7%, conventional (seven minute) slow inhalation induction with increasing sevoflurane concentration up to 5%, and induction with thiamylal i.v. METHODS: Twenty-four patients were randomly divided into three groups of eight. In Group A, anaesthesia was induced with tidal volume breathing of sevoflurane 7% (inspiratory concentration) and nitrous oxide 50% in oxygen (total flow; 6 l.min-1) for three minutes: Group B received conventional slow induction for seven minutes and increasing sevoflurane concentration by 0.5% every two or three breaths up to 5% with nitrous oxide 50% in oxygen: and Group C received 5 mg.kg-1 thiamylal with an inhalation of 100% oxygen. Blood pressure, heart rate, rate pressure product, and plasma concentrations of epinephrine and norepinephrine were measured. RESULTS: There were no changes in blood pressure before or after intubation in Group A (sevoflurane 7%) whereas both were increased in patients in Group C (thiamylal). Changes in heart rate and rate pressure product were not different for the two inhalation groups. Plasma epinephrine concentrations decreased in all the three groups. Norepinephrine concentrations were increased before intubation in both inhalation groups but not in the thiamylal group. CONCLUSION: Rapid induction of anaesthesia with sevoflurane 7% and tidal volume breathing for three minutes induced less haemodynamic changes than the other methods studied and has no inhibitory effect on sympathetic activity.

Adult↗

PubMed1988

A method for measuring tidal volume during high frequency jet ventilation.

A new method has been developed to measure tidal volume during high frequency jet ventilation. A pneumotachograph is placed in the expiratory limb of the breathing circuit. Using a model lung, the results from this method did not differ from the tidal volume calculated from pressure changes measured within the model lung. The results from the two methods correlated well (r = 0.99). The method enables the gas volumes entrained and spilled out of the airway during inspiration, true I:E ratios and mean driving pressures to be determined. The method is non-invasive and could easily be applied clinically.

High-Frequency Jet Ventilation↗

PubMed1997

A non-rebreathing coaxial anaesthesia system: dependence of end-tidal gas concentrations on fresh gas flow and tidal volume.

A non-rebreathing adaptation of the Bain coaxial anaesthesia circuit was developed in Nepal as a simple and economical anaesthetic system for underdeveloped countries. It was made by inserting a coaxial (Bain) tubing between an Ambu-E valve and an Ambu self-inflating bag. The present study examined the dependence of end-tidal gas concentrations on fresh gas flow and tidal volume during halothane/oxygen/air inhalation anaesthesia. Four levels of fresh gas flow with normocapnia (0.2-3 l.min-1) and three levels of tidal volume at a constant respiratory rate of 15 breath.min-1 (to achieve end-tidal carbon dioxide values of 4 +/- 0.5%, 5 +/- 0.5% and 6 +/- 0.5%) were introduced in random order. Twelve ASA class 1 and 2 adult patients having intra-abdominal or pelvic surgery were studied. With increasing fresh gas flow rates, there were proportionate increases in the end-tidal concentrations of oxygen and halothane; with decreasing tidal volume and therefore less air dilution, there were proportionate increases in the end-tidal concentrations of carbon dioxide, oxygen and halothane. Both effects were statistically and clinically significant. Thus, when this system is used as described, the end-tidal concentrations of oxygen and halothane are highly dependent upon both the fresh gas flow and the tidal volume.

Adult↗

PubMed1975

Sinus arrhythmia in man: influence of tidal volume and oesophageal pressure.

The effect of tidal volume (VT) and of the intrathoracic pressure (Poes) on the respiratory sinus arrhythmia (RSA) was studied in healthy subjects. They breathed into a spirometer with a VT of 1, 1.5, and 2 1, at a standardized, slow respiratory rate, 6-min-1 (A). Poes was varied by (B) adding a negative inspiratory pressure (NIP) of 5 cm of water and by (C) intermittent positive pressure ventilation (IPPV) at identical VT and respiratory frequency. In a separate study (D), intermittent negative pressure ventilation (INPV) was induced by applying negative pressure on the thorax. In A, increasing VT provoked an augmented RSA by a more marked tachycardia as well as bradycardia. On increasing the amplitude of Poes in B, RSA was somewhat more marked due to a lower minimum heart rate. When comparing respiratory cycles that had similar Poes but a different VT, the larger VT caused a slight increase in the RSA amplitude due to a more marked deceleration of the heart rate. IPPV almost abolished RSA, whereas INPV did not reduce the arrhythmia. It is concluded that pulmonary stretch reflexes to a minor extent contribute to RSA, whereas the hypothesis of a central nervous origin does not gain support. Cardiovascular reflexes remain the main possible cause of RSA.

Adult↗

PubMed1991

Accuracy of respiratory inductive plethysmograph in measuring tidal volume during sleep.

Respiratory inductance plethysmography (RIP) has been widely used to measure ventilation during sleep, but its accuracy in this role has not been adequately tested. We have thus examined the accuracy of the RIP by comparing tidal volume measured with RIP with that measured by a pneumotachograph in eight unrestrained normal subjects during sleep. We have also studied the effect of posture on the accuracy of the RIP. In all sleep stages the correlation between RIP tidal volume measurements and expired volume showed relatively poor correlations (mean r = 0.49-0.60), and the bias of the measurements varied widely. Changes in posture altered the correlations between the two measurements, with no systematic differences between positions. When the subjects resumed a position, the 95% confidence intervals of tidal volume measurement did not overlap the original confidence limits in that posture on 13 of 25 occasions. This study shows that the RIP does not accurately measure tidal volume during sleep in unrestrained subjects and should only be used for semiquantitative assessment of ventilation during sleep.

Adult↗

PubMed2002

Modeling the effect of progressive endotracheal tube occlusion on tidal volume in pressure-control mode.

UNLABELLED: A recognized hazard of prolonged endotracheal intubation is progressive airway occlusion resulting from deposition of secretions on the inner surface of the endotracheal tube (ETT). When volume-controlled ventilation is used, progressive ETT occlusion may be detected by monitoring the difference between peak and plateau airway pressures. In pressure-controlled modes, however, inspiratory airway pressures are preset and thus cannot act as a warning indicator. Instead, changes in delivered tidal volumes may aid the diagnosis of ETT occlusion. To determine whether tidal volume monitoring effectively detects progressive ETT occlusion, we mathematically modeled the response of a ventilator operating in pressure-controlled mode to increasing airway resistance. To corroborate our model, we then bench-tested the Siemens 300 and Puritan-Bennett 7200 ventilators by using a test lung and a series of ETTs ranging in size from 9.0 to 3.5 mm inner diameter to simulate progressive occlusion. We found that when pressure-controlled mode was used, progressive ETT occlusion did not reduce delivered tidal volumes until occlusion was nearly complete. We conclude that prolonged use of pressure-controlled mode may allow significant ETT obstruction to build up undetected, risking complete ETT occlusion and complicating the perioperative care of patients ventilated with this mode. IMPLICATIONS: Although increasing airway pressures during volume-controlled ventilation allow early recognition of endotracheal tube (ETT) obstruction, airway pressures with pressure-controlled ventilation are fixed. We found during tests of two intensive care unit ventilators that although ETT obstruction reduces delivered tidal volumes during pressure-controlled ventilation, reductions do not occur until occlusion is advanced.

Algorithms↗