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PubMed1976

The role of the fusimotor system with respect to the contribution of the diaphragm and the intercostal muscles to the respiratory tidal volume.

The efferent electrical activity in the phrenic nerve can be quantified in such a way that it gives a good correlation to tidal volume. After administration of the drug benzoctamine this relationship changes: more phrenic nerve activity is needed for the same tidal volume. No changes were found in the neuro-muscular transmission from the phrenic nerve to the diaphragm. There was no alteration in dynamic compliance of the lungs or in airway resistance. The afferent phrenic nerve activity from proprioceptors in the diaphragm did not change. It seems unlikely that respiratory neurons in the brainstem were affected since the sensitivity of the respiratory system to CO2 did not change. It is known that the tonic fusimotoneuron activity is suppressed at a supraspinal level by benzoctamine. Since intercostal muscles have muscle spindles and the diaphragm hardly has any, the intercostal muscle activity will be affected more than diaphragmatic activity by benzoctamine. This could actually be shown by quantifying the electromyogram of inspiratory external intercostal muscles. The tidal volume regulation is controlled by the vagal feedback loop. In order to reach a certain tidal volume after administration of benzoctamine, the contribution of the diaphragm has to increase because the activity of the intercostal muscles is diminished.

Animals↗

PubMed1980

Practical implementation of the barometric method for measurement of tidal volume.

The barometric method is unique in permitting measurement of tidal volume in a totally noninvasive manner. Its application and accuracy have been limited by several complex problems. These include control of inspired gas composition, base-line stability, and asymmetry of processes occurring during inspiration and expiration. A new method is described that addresses these problems and facilitates long-term measurements. New calculations, which avoid previous errors that caused the method to systematically underestimate tidal volume, are illustrated.

Animals↗

PubMed1990

Influence of tidal volume on respiratory compliance in anesthetized infants and young children.

Recent studies have suggested a close association between total respiratory compliance (Crs) and tidal volume in anesthetized paralyzed infants who are being artificially ventilated. To investigate this further, the multiple occlusion technique was used to measure Crs in 20 anesthetized infants and young children (aged 1-25 mo) before elective surgery. Measurements were made after intubation 1) during spontaneous breathing (SB), 2) after administration of a non-depolarizing muscle relaxant with tidal volume and frequency mimicking that during SB, and 3) with the child still paralyzed but tidal volume approximately double that during SB. Compared with values obtained during SB, there was no significant change in Crs after paralysis when ventilation matched the child's own pattern (P greater than 0.2). When ventilated with the larger tidal volumes, the infants showed a highly significant increase in Crs (mean 62%, range 14-158%, P less than 0.0001). These results may have implications not only for studies performed during anesthesia but also when infants were monitored in the intensive care setting. Values of Crs obtained in ventilated infants may reflect both the mechanical behavior of the respiratory system and the pattern of ventilation at the time of measurement.

Anesthesia↗

PubMed2006

Unrestrained acoustic plethysmograph for measuring tidal volume in mice.

The traditional method for measurement of tidal volume in unrestrained mice relies on pressure changes induced by a freely respiring animal in a whole body plethysmograph. These changes have been assumed to be the result of thermo-hygrometric differences between respired air and gas within the chamber. It is known, however, that gas compression in the lung can also contribute significantly to changes in plethysmograph pressure. This study describes an acoustic plethysmograph for mice that is capable of measuring the tidal volume time series without the errors associated with the traditional method. The plethysmograph was designed as a resonating cavity at a fixed frequency. It had a sharp resonant peak and was tuned so that changes in body volume produced nearly linear changes in sound amplitude. The plethysmograph was tested with a water filled balloon connected to a syringe pump. The volume of the balloon was varied as a triangle wave with an amplitude of 250 microL. The RMS error between measured and delivered volume was 4.43 microL. A volume step test, performed to assess the response time of the system, showed that the plethysmograph responded in less than one millisecond.

Acoustics↗

PubMed2003

Tidal volume, cardiac output and functional residual capacity determine end-tidal CO2 transient during standing up in humans.

In man assuming the upright position, end-tidal P(CO(2)) (P(ETCO(2))) decreases. With the rising interest in cerebral autoregulation during posture change, which is known to be affected by P(ETCO(2)), we sought to determine the factors leading to hypocapnia during standing up from the supine position. To study the contribution of an increase in tidal volume (V(T)) and breathing frequency, a decrease in stroke volume (SV), a ventilation-perfusion (V/Q) gradient and an increase in functional residual capacity (FRC) to hypocapnia in the standing position, we developed a mathematical model of the lung to follow breath-to-breath variations in P(ETCO(2)). A gravity-induced apical-to-basal V/Q gradient in the lung was modelled using nine lung segments. We tested the model using an eight-subject data set with measurements of V(T), pulmonary O(2) uptake and breath-to-breath lumped SV. On average, the P(ETCO(2)) decreased from 40 mmHg to 36 mmHg after 150 s standing. Results show that the model is able to track breath-to-breath P(ETCO(2)) variations (r(2)= 0.74, P P 0.05). Model parameter sensitivity analysis demonstrates that the decrease in P(ETCO(2)) during standing is due primarily to increased V(T), and transiently to decreased SV and increased FRC; a slight gravity-induced V/Q mismatch also contributes to the hypocapnia. The influence of cardiac output on hypocapnia in the standing position was verified in experiments on human subjects, where first breathing alone, and then breathing, FRC and V/Q were controlled.

Adult↗

PubMed2000

Inaccuracy of tidal volume delivered by home mechanical ventilators.

Ideally, the inspired (tidal) volume (V(T)) provided by a volume-controlled ventilation device should not change when the pressure imposed on the ventilator varies. A bench study evaluation of V(T) versus pressure was performed on 10 commercially available devices. The difference between the desired V(T) and the observed V(T) reached 100 mL for some devices when inspiratory resistance was at its lowest, rising to 150 mL when inspiratory resistance was increased to obtain peak airway pressure of 60 cmH2O. The present data indicate that some home ventilators are inaccurate in delivering the preset tidal volume when the pressure imposed on the ventilator is increased to simulate high airway resistance.

Airway Resistance↗

PubMed2003

Oxygenation using tidal volume breathing after maximal exhalation.

UNLABELLED: We compared, in volunteers, the oxygenation achieved by tidal volume breathing (TVB) over a 3-min period after maximal exhalation with that achieved by TVB alone. Twenty-three healthy volunteers underwent the two breathing techniques in a randomized order. A circle absorber system with an oxygen flow of 10 L/min was used. The end-expiratory oxygen concentration (EEO(2)) was monitored at 15-s intervals up to 3 min. TVB after maximal exhalation produced EEO(2) values of 68% +/- 5%, 75% +/- 5%, and 79% +/- 4% at 30, 45, and 60 s, respectively, which were significantly larger (P < 0.05) than the corresponding values obtained with TVB alone (58% +/- 5%, 66% +/- 6%, and 71% +/- 5%, respectively). In both techniques, the EEO(2) increased exponentially, with time constants of 35 s during TVB after maximal exhalation versus 58 s during TVB without prior maximal exhalation. In conclusion, maximal exhalation before TVB can hasten preoxygenation by decreasing the nitrogen content of the functional residual capacity, with a consequent increase of EEO(2) to approximately 70% in 30 s and 80% in 60 s. IMPLICATIONS: Oxygenation by using maximal exhalation before tidal volume breathing produced a significantly faster increase in end-expiratory oxygen concentration than oxygenation with tidal volume breathing alone.

Adult↗

PubMed2002

Are tidal volume measurements in neonatal pressure-controlled ventilation accurate?

Bedside pulmonary mechanics monitors (PMM) have become useful in ventilatory management in neonates. These monitors are used more frequently due to recent improvements in data-processing capabilities. PMM devices are often part of the ventilator or are separate units. The accuracy and reliability of these systems have not been carefully evaluated. We compared a single ventilatory parameter, tidal volume (V(t)), as measured by several systems. We looked at two freestanding PMMs: the Ventrak Respiratory Monitoring System (Novametrix, Wallingford, CT) and the Bicore CP-100 Neonatal Pulmonary Monitor (Allied Health Care Products, Riverside, CA), and three ventilators with built-in PMM: the VIP Bird Ventilator (Bird Products Corp., Palm Springs, CA), Siemens Servo 300A (Siemens-Elema AB, Solna, Sweden), and Drager Babylog 8000 (Drager, Inc., Chantilly, VA). A calibrated syringe (Hans Rudolph, Inc., Kansas City, MO) was used to deliver tidal volumes of 4, 10, and 20 mL to each ventilator system coupled with a freestanding PMM. After achieving steady state, six consecutive V(t) readings were taken simultaneously from the freestanding PMM and each ventilator. In a second portion of the bench study, we used pressure-control ventilation and measured exhaled tidal volume (V(te)) while ventilating a Bear Test Lung with the same three ventilators. We adjusted peak inspiratory pressure (PIP) under controlled conditions to achieve the three different targeted tidal volumes on the paired freestanding PMM. Again, six V(te) measurements were recorded for each tidal volume. Means and standard deviations were calculated.The percentage difference in measurement of V(t) delivered by calibrated syringe varied greatly, with the greatest discrepancy seen in the smallest tidal volumes, by up to 28%. In pressure control mode, V(te) as measured by the Siemens was significantly overestimated by 20-95%, with the biggest discrepancy at the smallest V(te), particularly when paired with the Bicore PMM. V(te), as measured by the VIP Bird and Drager paired with the Ventrak PMM, had a tendency to underestimate V(t) by up to 25% at the smallest V(te). However, when paired with the Bicore PMM, these same two ventilators read over target by up to 18%. Under controlled laboratory conditions, we demonstrated that true delivered V(te), as measured by the three ventilators and two freestanding PMM, differed markedly. In general, decreasing dynamic compliance of the tubing was not associated with greater inaccuracy in V(te) measurements.

Calibration↗

PubMed1988

High inflation pressure pulmonary edema. Respective effects of high airway pressure, high tidal volume, and positive end-expiratory pressure.

The respective roles of high pressure and high tidal volume to promote high airway pressure pulmonary edema are unclear. Positive end-expiratory pressure (PEEP) was shown to reduce lung water content in this type of edema, but its possible effects on cellular lesions were not documented. We compared the consequences of normal tidal volume ventilation in mechanically ventilated rats at a high airway pressure (HiP-LoV) with those of high tidal volume ventilation at a high (HiP-HiV) or low (LoP-HiV) airway pressure and the effects of PEEP (10 cm H2O) on both edema and lung ultrastructure. Pulmonary edema was assessed by extravascular lung water content and microvascular permeability by the drug lung weight and the distribution space of 125I-labeled albumin. HiP-LoV rat lungs were not different from those of controls (7 cm H2O peak pressure ventilation). By contrast, the lungs from the groups submitted to high volume ventilation had significant permeability type edema. This edema was more pronounced in LoP-HiV rats. It was markedly reduced by PEEP, which, in addition, preserved the normal ultrastructural aspect of the alveolar epithelium. This was in striking contrast to the diffuse alveolar damage usually encountered in this type of edema. To our knowledge, this constitutes the first example of a protective effect of PEEP during permeability edema.

Animals↗

PubMed1979

Experimental studies on artificial ventilation using a tidal volume ventilator. Mechanics and dynamics of ventilation.

In 24 piglets (2.7-24.5 kg b.w.), the mechanics of ventilation, the accuracy of dosage of respiratory volumes, and the influence of the ventilator's volume/pressure characteristics (Cvent, "internal compliance") on the dynamic course of insufflation were studied. A linear relationship was shown to exist between tidal volume and end-inspiratory tracheal pressure and between tidal volume and insufflation time. The insufflation time was reduced to about 50% of previously registered values. The error between set and registered tidal volume was found to be 6.0 +/- 2.7%. During the insufflation a linear relationship was found between the instant amount of delivered breathing gas and the corresponding endotracheal pressure change. The ventilator's Cvent did (and body size, total compliance and tidal volume did not) significantly influence the size of the direction coefficient for the linear instantaneous volume/pressure relationship, the magnitude of tracheal peak pressure and a short insufflation time, and vice versa. The use of greater power from the ventilator resulted in a significant shortening of the duration of insufflation and vice versa. The duration of insufflation is the parameter of choice in evaluating the efficiency of the ventilatory equipment. When the ventilator's performance is defined, measurements of the duration of insufflation may enable evaluation of conditions within the lungs.

Animals↗

PubMed2005

Acute effects of tidal volume strategy on hemodynamics, fluid balance, and sedation in acute lung injury.

OBJECTIVE: To examine the effects of mechanical ventilation with a tidal volume of 6 mL/kg compared with 12 mL/kg predicted body weight on hemodynamics, vasopressor use, fluid balance, diuretics, sedation, and neuromuscular blockade within 48 hrs in patients with acute lung injury and acute respiratory distress syndrome. DESIGN: Retrospective analysis of a previously conducted randomized, clinical trial. SETTING: Two adult intensive care units at a tertiary university medical center and a large county hospital. PATIENTS: One hundred eleven patients who were enrolled in the National Institutes of Health ARDS Network trial at the University of California, San Francisco. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Compared with 12 mL/kg predicted body weight, treatment with a tidal volume of 6 mL/kg predicted body weight had no adverse effects on hemodynamics. There were also no differences in the need for supportive therapies, including vasopressors, intravenous fluids, or diuretics. In addition, there were no differences in body weight, urine output, and fluid balance. Finally, there was no difference in the need for sedation or neuromuscular blockade between the two tidal volume protocols. CONCLUSIONS: When compared with ventilation with 12 mL/kg predicted body weight, patients treated with the lung-protective 6 mL/kg predicted body weight tidal volume protocol had no difference in their supportive care requirements. Therefore, concerns regarding potential adverse effects of this protocol should not preclude its use in patients with acute lung injury or the acute respiratory distress syndrome.

Adult↗

PubMed1988

Measurement of tidal volume during high frequency ventilation by impedance plethysmography.

Electrical impedance plethysmography was evaluated in lambs as a method of measuring tidal volume (VT). Over tidal volumes ranging from 15 to 414% of estimated dead space, and frequencies of 300 to 1000 breaths/min, correlation between VT measured by the impedance technique and VT measured by whole-body plethysmography was 0.98. Above 600 breaths/min, the correlation between the two methods was 0.94. Independent calibration of the impedance technique using a pneumotachograph at conventional rates of ventilation yielded absolute values of VT which closely corresponded to values obtained with the whole-body plethysmograph (slope = 1.05, intercept = 1.4 ml, r = 0.99). These results support the potential utility of impedance plethysmography in clinical applications of high frequency ventilation.

Animals↗

PubMed2001

Immediate effects of positive end-expiratory pressure and low and high tidal volume ventilation upon gas exchange and compliance in patients with acute lung injury.

BACKGROUND: Protective ventilation, in general, includes low tidal volume ventilation and maintaining end-inspiratory plateau pressures less than 35 cmH2O. Recent clinical studies have determined that such an approach results in improved survival in patients with moderate to severe acute lung injury and acute respiratory distress syndrome. However, experimental evidence suggests that repeated end-expiratory collapse and reexpansion contributes to ventilator-induced lung injury. We sought to determine the immediate effects of specific tidal volume-PEEP combinations upon oxygenation and static compliance in patients with moderate to severe acute lung injury. METHODS: Fourteen patients were prospectively studied and were treated with each of 10 tidal volume-PEEP combinations, applied in random order. After 5 minutes at each tidal volume-PEEP combination, PaO2/FIO2 and static compliance were recorded. Comparisons were made between low and high tidal volume ventilation as well as across five PEEP levels. RESULTS: At both low (6 mL/kg) and high (10 mL/kg) tidal volume ventilation, PaO2/FIO2 increased with increasing PEEP, up to 20 cmH2O. Similar changes in static compliance were not evident. Static compliance was highest at PEEP of 10 and 15 cmH2O, regardless of tidal volume. With PEEP set at 5 cmH2O, static compliance was significantly lower with 6 mL/kg than with 10 mL/kg tidal volumes. Overall, static compliance was lowest for both tidal volume conditions with PEEP set at 25 cmH2O. CONCLUSION: Low tidal volume ventilation with PEEP set at 5 cmH2O results in poor oxygenation and compliance in patients with moderate to severe acute lung injury. Similarly, PEEP set at 25 cmH2O did not improve oxygenation or compliance.

Adolescent↗

PubMed1980

[Dependence of the anatomical dead space on the tidal volume and on the endexpiratory lung volume: dynamic behaviour and stabilization of the bronchiolar tone (author's transl)].

The anatomical dead space was measured in dependence on the tidal volume and on the endexpiratory lung volume (respiratory level). A new method, the method of dead air plateau, was employed. The dead space increases with tidal volume (4 ml/100 ml). It is not dependent on the respiratory level. This was also directly shown in breathing manoeuvres changing the respiratory level rectangularly. In such manoeuvres a stabilization process can be seen. The same results give resistance measurements (oscillatory method). Values are taken in the endinspiratory state. This corresponds to the dead space volume. The 70% time of the stabilization reaction can be estimated, it is 20 sec. Taking this time into account, it is well understood that dead space volume is dependent on the tidal volume, but not dependent on the respiratory level. This time also makes evident that the often mentioned history of lung parameters lasts approximately 20 sec. The biological significance of the stabilization is discussed.

Bronchi↗

PubMed1997

Tidal volume effects on surfactant treatment responses with the initiation of ventilation in preterm lambs.

We hypothesized that initiation of ventilation in preterm lambs with high volumes would cause lung injury and decrease the subsequent response to surfactant treatment. Preterm lambs were randomized to ventilation for 30 min after birth with 5 ml/kg (VT5), 10 ml/kg (VT10), or 20 ml/kg (VT20) tidal volumes and then ventilated with approximately 10 ml/kg tidal volumes to achieve arterial PCO2 values of approximately 50 Torr to 6 h of age. VT20 lambs had lower compliances, lower ventilatory efficiencies, higher recoveries of protein, and lower recoveries of surfactant in alveolar lavages and in surfactant that had decreased compliances when tested in preterm rabbits than VT5 or VT10 lambs. Other lambs randomized to treatment with surfactant at birth and ventilation with 6, 12, or 20 ml/kg tidal volumes for 30 min had no indicators of lung injury. An initial tidal volume of 20 ml/kg decreased the subsequent response to surfactant treatment, an effect that was prevented with surfactant treatment at birth.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2006

Volume-targeted modes of modern neonatal ventilators: how stable is the delivered tidal volume?

OBJECTIVE: Volume-targeted modes are designed to deliver a constant tidal volume (V(t)) at lowest possible pressure independently of changes in compliance, resistance, and leak of the respiratory system. We examined whether these volume-targeted modes respond rapidly enough to sudden changes in respiratory mechanics (e.g., selective intubation, surfactant administration, endotracheal tube kinking, de-kinking, obstruction), resulting in insufficient or excessive V(t) delivery. DESIGN AND SETTING: Bench study of six neonatal ventilators in the volume-targeted mode simulating preterm and full-term infant settings on a test lung. MEASUREMENTS AND RESULTS: Breath-to-breath expiratory V(t) were measured after rapid compliance, resistance, and leak changes. Under our test settings all ventilators showed important volume overshooting following rapid increase in compliance or decrease in resistance. Between one and 16 inflations were required to return to the set V(t). Some ventilators delivered inaccurate V(t) under steady state condition while others showed considerable breath-to-breath V(t) variability. CONCLUSIONS: We observed inaccurate V(t) delivery under specific conditions as well as immediate and sometimes prolonged volume overshooting after a rapid respiratory system compliance increase or resistance decrease in volume-targeted modes of modern neonatal ventilators. Similar discrepancies between the set V(t) and the delivered inflations can be harmful in clinical situations, especially in newborns. Their clinical relevance needs to be clarified with safety studies in the neonatal population and we encourage manufacturers to further improve the ventilators algorithms.

Equipment Design↗

PubMed1984

Accuracy of respiratory inductive plethysmograph over wide range of rib cage and abdominal compartmental contributions to tidal volume in normal subjects and in patients with chronic obstructive pulmonary disease.

We assessed the accuracy of the respiratory inductive plethysmograph in the supine position to spirometry by the two-body position, least squares calibration and single-body position, isovolume calibration procedures. The comparison was carried out simultaneously in normal subjects breathing naturally and with voluntarily controlled abdominal or thoracic breathing, and in patients with COPD breathing naturally and with voluntarily controlled abdominal breathing patterns. In both groups, there was no significant difference in estimation of tidal volume between the 2 calibration procedures for the various breathing patterns. There was greater deviation from spirometric tidal volume values for both calibration methods in patients with COPD during abdominal than during natural breathing. In the normal subjects, agreement between the rib cage and abdominal partitioning of tidal volume for both calibration methods was good, but in the patients with COPD there was greater variability. In normal subjects, over a wide range of rib cage and abdominal compartmental contributions to tidal volume, either calibration procedure appears satisfactory. For patients with COPD, if large changes occur in the distribution of rib cage and abdominal contributions to tidal volume, then validation of respiratory inductive plethysmography to spirometry must be rechecked.

Abdomen↗

PubMed1999

Effects of smaller tidal volumes during basic life support ventilation in patients with respiratory arrest: good ventilation, less risk?

OBJECTIVE: When ventilating an unintubated patient in cardiac or respiratory arrest, smaller tidal volumes of 500 ml instead of 800-1200 ml may be beneficial to decrease peak airway pressure, and to minimise stomach inflation. The purpose was to determine the effects of small (approximately 500 ml) versus large (approximately 1000 ml) tidal volumes given with paediatric versus adult self-inflatable bags and approximately 50% oxygen on respiratory parameters in patients during simulated basic life support ventilation. METHODS: While undergoing induction of anaesthesia, patients were randomised to three minutes of ventilation with either an adult (n = 40) or paediatric (n = 40) self-inflatable bag. RESULTS: When compared with an adult self-inflatable bag, the paediatric bag resulted in significantly lower mean (+/- standard deviation) exhaled tidal volume (365 +/- 55 versus 779 +/- 122 ml; P < 0.0001), peak airway pressure (20 +/- 2 versus 25 +/- 5 cm H2O; P < 0.0001), but comparable oxygen saturation (97 +/- 1% versus 98 +/- 1%; NS (nonsignificant)). Stomach inflation occurred in five of 40 patients ventilated with an adult self-inflatable bag, but in no patients who were ventilated with a paediatric self-inflatable bag (P = 0.054). CONCLUSION: Administering smaller tidal volumes with a paediatric instead of an adult self-inflatable bag in unintubated adult patients with respiratory arrest maintains good oxygenation and carbon dioxide elimination while decreasing peak airway pressure, which makes stomach inflation less likely.

Adult↗