Indexes Of Respiratory Effort Research Articles

Physiologic Effects of High-Flow Nasal Cannula in Healthy Subjects.

High-flow nasal cannula (HFNC) is increasingly used in the management of acute and chronic respiratory failure. Little is known about the optimal settings for HFNC. This study was designed to assess the dose effect of HFNC on respiratory effort indexes and respiratory patterns in spontaneously breathing adults. A randomized controlled crossover study was conducted in 10 healthy subjects. Five experimental conditions were evaluated: baseline with no therapy; 5 L/min with conventional nasal prongs; and HFNC at 20, 40, and 60 L/min. The primary outcomes were the indexes of respiratory effort (ie, esophageal pressure swing [ΔPes], esophageal pressure-time product, and work of breathing). Secondary outcomes included breathing pattern parameters and blood gases. Dead-space ventilation and washout were calculated based on minute ventilation, breathing frequency, and Radford equations. ΔPes increased from median (interquartile range [IQR] 3.2 (2.2-3.6) cm H2O at baseline to median (IQR) 5.7 (4.6-6.8) cm H2O at 60 L/min (P < .001). Neither esophageal pressure-time product nor work of breathing were modified during the tested conditions. The minute volume was significantly reduced at 40 and 60 L/min compared with baseline (P = .04), mostly driven by an important and dose-dependent reduction in breathing frequency, from median (IQR) 16 (15-18) breaths/min at baseline, to median (IQR) 8 (7-10) breaths/min at 60 L/min (P < .001). Capillary [Formula: see text] was stable in all the tested conditions. The calculated dead-space ventilation was reduced by half with HFNC. HFNC did not significantly modify work of breathing in healthy subjects. However, a significant reduction in the minute volume was achieved, capillary [Formula: see text] remaining constant, which suggests a reduction in dead-space ventilation with flows > 20 L/min. (ClinicalTrials.gov registration NCT02495675).

Impact of Gas Masks on the Work of Breathing and Breathing Pattern in Subjects With Stable COPD.

The gas mask constitutes the main respiratory protective equipment in a chemical, biological, radiological, or nuclear environment. The aim of the study was to evaluate the impact of the gas mask on respiratory pattern, gas exchange, and indexes of respiratory effort in patients with moderate to severe stable COPD. Crossover evaluation with 3 randomized-order, 10-min conditions: at rest and with and without a gas mask using 2 different filtered cartridges, each with a distinct inspiratory resistance (cartridge A = 3.5 cm H2O; cartridge B = 2.2 cm H2O, both at 1 L/s). The study involved 8 subjects with COPD, and breathing patterns, indexes of respiratory effort, and capillary blood gases were evaluated. Comparisons of these parameters were made between the tested conditions. Mean subject age was 69 y, and mean FEV1 = 1.3 L (47% predicted). Short-term utilization of the gas mask was associated with a significant increase in the indexes of effort in comparison to baseline without a mask. The esophageal product-time product significantly increased in comparison with baseline (cartridge A = 281 ± 65 cm H2O/s/min, cartridge B = 253 ± 47 cm H2O/s/min, and baseline = 184 ± 46 cm H2O/s/min, P < .001). There were negligible changes in the breathing pattern and gas exchange. Indexes of respiratory effort increased slightly in subjects with stable COPD while using a gas mask. This effect was likely related to increased inspiratory resistance when the mask was worn. These data are reassuring for the potential short-duration use of such protection for patients with moderate to severe COPD.

Impact of Gas Masks on Work of Breathing, Breathing Patterns, and Gas Exchange in Healthy Subjects.

The gas mask is used to protect military and non-military personnel exposed to respiratory hazards (chemical, biologic, radiologic, and nuclear agents). The objective was to evaluate the impact of the gas mask on indexes of respiratory effort and breathing patterns in a human model because no data exist. The design of the study was a crossover evaluation with four 10-min conditions in a randomized order: with and without wearing the gas mask when at rest and when exerting a standardized effort. During the studied conditions, 14 healthy subjects were evaluated for breathing patterns, indexes of respiratory effort (work of breathing, pressure-time product for esophageal pressure, and esophageal pressure swing) and capillary blood gases. Continuous SpO2 was recorded during the tested conditions. The indexes of respiratory effort significantly increased when subjects wore the gas mask under the tested conditions (at rest and during effort). The work of breathing was significantly augmented with the mask (at rest, 0.40 ± 0.32 J/cycle vs 0.25 ± 0.10 J/cycle; effort, 5.96 ± 3.32 J/cycle vs 4.43 ± 2.50 J/cycle; P < .001). The other indexes of effort (esophageal pressure-time product and esophageal swing were all significantly increased, from 30 to 60%, with a gas mask in comparison with at baseline without a gas mask). The impact on breathing patterns and PaCO2 was limited, without significant differences. Moderate hypoxemia was present during effort and was not increased by the gas mask. This study demonstrated a substantial increase in the indicies of respiratory effort both at rest and during exercise with a gas mask. Our measurements and findings may be referred in future research and development studies in this field. (ClinicalTrials.gov registration NCT02782936.).

Effects of High-Flow Nasal Cannula on the Work of Breathing in Patients Recovering From Acute Respiratory Failure.

High-flow nasal cannula is increasingly used in the management of respiratory failure. However, little is known about its impact on respiratory effort, which could explain part of the benefits in terms of comfort and efficiency. This study was designed to assess the effects of high-flow nasal cannula on indexes of respiratory effort (i.e., esophageal pressure variations, esophageal pressure-time product/min, and work of breathing/min) in adults. A randomized controlled crossover study was conducted in 12 patients with moderate respiratory distress (i.e., after partial recovery from an acute episode, allowing physiologic measurements). Institut Universitaire de Cardiologie et de Pneumologie de Québec, QC, Canada. Twelve adult patients with respiratory distress symptoms were enrolled in this study. Four experimental conditions were evaluated: baseline with conventional oxygen therapy and high-flow nasal cannula at 20, 40, and 60 L/min. The primary outcomes were the indexes of respiratory effort (i.e., esophageal pressure variations, esophageal pressure-time product/min, and work of breathing/min). Secondary outcomes included tidal volume, respiratory rate, minute volume, dynamic lung compliance, inspiratory resistance, and blood gases. Esophageal pressure variations decreased from 9.8 (5.8-14.6) cm H2O at baseline to 4.9 (2.1-9.1) cm H2O at 60 L/min (p = 0.035). Esophageal pressure-time product/min decreased from 165 (126-179) to 72 (54-137) cm H2O • s/min, respectively (p = 0.033). Work of breathing/min decreased from 4.3 (3.5-6.3) to 2.1 (1.5-5.0) J/min, respectively (p = 0.031). Respiratory pattern variables and capillary blood gases were not significantly modified between experimental conditions. Dynamic lung compliance increased from 38 (24-64) mL/cm H2O at baseline to 59 (43-175) mL/cm H2O at 60 L/min (p = 0.007), and inspiratory resistance decreased from 9.6 (5.5-13.4) to 5.0 (1.0-9.1) cm H2O/L/s, respectively (p = 0.07). High-flow nasal cannula, when set at 60 L/min, significantly reduces the indexes of respiratory effort in adult patients recovering from acute respiratory failure. This effect is associated with an improvement in respiratory mechanics.

Adaptive Support and Pressure Support Ventilation Behavior in Response to Increased Ventilatory Demand

Dual-control modes of ventilation adapt the pressure delivery to keep a volume target in response to changes in respiratory mechanics, but they may respond poorly to changes in ventilatory demand. Adaptive support ventilation (ASV), a complex minute volume-targeted pressure-regulated ventilation, was compared to adaptive pressure ventilation (APV), a dual-mode in which the pressure level is adjusted to deliver a preset tidal volume, and to pressure support ventilation (PSV) when facing an increase in ventilatory demand. A total of 14 intensive care unit patients being weaned off mechanical ventilation were included in this randomized crossover study. The effect of adding a heat-and-moisture exchanger to augment circuit dead space was assessed with a same fixed level of ASV, PSV, and APV. Arterial blood gases, ventilator response, and patient respiratory effort parameters were evaluated at the end of the six periods. Adding dead space significantly increased minute ventilation and PaCO2 values with the three modes. Indexes of respiratory effort (pressure-time index of respiratory muscles and work of breathing) increased with all ventilatory modes after dead-space augmentation. This increase was significantly greater with APV than with PSV or ASV (P < 0.05). The assistance delivered during APV decreased significantly with dead-space from 12.7 +/- 2.6 to 6.7 +/- 1.4 cm H2O, whereas no change occurred with ASV and PSV. ASV and PSV behaved differently but ended up with similar pressure level facing acute changes in ventilatory demand, by contrast to APV (a simple volume-guaranteed pressure-control mode), in which an increase in ventilatory demand results in a decrease in the pressure support provided by the ventilator.

Physiological effects of different interfaces during noninvasive ventilation for acute respiratory failure*

To test the short-term physiologic effects (indexes of respiratory effort, ventilation, and gas exchange), leaks, patient-ventilator asynchrony, and comfort of four noninvasive ventilation (NIV) facial, oronasal, or oral interfaces with major differences in internal volume. Prospective, short-term, crossover randomized physiologic study. Medical intensive care unit in a university hospital. Fourteen consecutive patients receiving NIV for either hypoxemic (n = 7) or hypercapnic (n = 7) acute respiratory failure. Four interfaces, tested randomly over consecutive sequences, had very high (977 mL), high (163 mL), moderate (84 mL), or virtually no internal volume (mouthpiece). The pressure level was increased in two patients with the larger mask, and was decreased in all patients when using the mouthpiece. Despite differences in internal volume, no apparent dead space effect was observed on minute ventilation, work of breathing, or arterial CO2 levels. Compared with baseline, NIV was uniformly successful in reducing indexes of respiratory effort: the pressure-time product of the respiratory muscles decreased from a median (25th-75th interquartile range) of 179 (158-285) cm H2O.sec.min to values between 91 and 111 during NIV, with no differences between masks (p = 0.84). Few differences were observed in terms of arterial blood gases and breathing pattern. Leaks and patient-ventilator asynchronies were greater with the mouthpiece, and comfort with this interface was deemed poor for most patients. The internal volume of the masks had no apparent short-term dead space effect on gas exchange, minute ventilation, or patient's effort, suggesting that, with the exception of mouthpiece, interfaces may be interchangeable in clinical practice provided adjustment of the ventilatory device parameters are performed.

Volume-guaranteed pressure-support ventilation facing acute changes in ventilatory demand

To compare volume support ventilation (VSV) in which the pressure support level is continuously adjusted to deliver a preset tidal volume, with pressure support ventilation (PSV), in terms of patient behavior and ventilator response when ventilatory demand was increased by addition of dead space to the circuit. Randomized cross-over study in an intensive care unit university hospital. We assessed in ten patients being weaned off mechanical ventilation the effect of increasing the ventilatory demand by adding a heat-and-moisture exchanger to augment the dead space with a fixed level of PSV and VSV. Arterial blood gases, breathing pattern, and respiratory effort parameters at the end of each of the four steps. Adding dead space significantly increased minute ventilation and PaCO2 values with both PSV and VSV. Indexes of respiratory effort (pressure-time index of respiratory muscles and work of breathing) increased with both ventilatory modes after dead-space augmentation. This increase was 2.5-4 times with VSV than with PSV and induced overt respiratory distress in two patients. The assistance delivered during VSV decreased significantly after dead-space augmentation, from 15.0+/-6.5 to 9.1+/-4.8 cmH2O, whereas no change occurred with PSV. With a fixed level of VSV, but not of PSV, an increase in ventilatory demand results in a decrease in the pressure support provided by the ventilator, opposite to the desired response. VSV may conceivably result in respiratory distress in clinical settings.

Respiratory Effort During Obstructive Sleep Apnea: Role of Age and Sleep State

To evaluate the patients' individual characteristics predictive of the degree of respiratory effort developed during obstructive sleep apneas (OSAs). Prospective consecutive sample, collection of clinical and polysomnographic data. University teaching hospital. One hundred sixteen consecutive OSA patients with clinical symptoms of OSA and more than 20 apneas per hour of sleep. Anthropomorphic data, daytime blood gas values, and polysomnographic data. From esophageal pressure measurements during sleep, three indexes of respiratory effort during OSAs were derived: the maximal end-apneic esophageal pressure swing (PesMax), the increase in esophageal pressure swing (deltaPes) during the apnea, and its ratio to apnea duration (RPes). The indexes of respiratory effort were significantly lower in rapid eye movement (REM) than in non-REM sleep (PesMax: 50.9+/-2.5 vs 39.6+/-1.9 cm H2O, p<0.001; deltaPes: 30.9+/-1.7 vs 23.4+/-1.4 cm H2O, p<0.001; RPes: 1.05+/-0.05 vs 0.53+/-0.03 cm H2O/s, p<0.001); therefore, a separate analysis was conducted in non-REM and in REM sleep. Indexes were also significantly lower in subgroups of older as compared to younger patients (PesMax: 55.6+/-3.5 vs 40.0+/-2.2 cm H2O, p<0.001; deltaPes: 34.2+/-2.3 vs 24.1+/-1.6 cm H2O, p=0.001; RPes: 1.21+/-0.08 vs 0.8+/-0.05 cm H2O/s, p<0.001). The three indexes were closely correlated with each other and only PesMax correlation data are reported. In non-REM sleep, age was the most important single independent correlate of PesMax (r=-0.37, p=0.000). In REM sleep, the apnea-related hypoxemia, apnea duration, and age were the main contributors to the variance of PesMax. Respiratory effort in response to upper airway occlusion in OSA patients is lower in REM than in non-REM sleep and decreases with increasing age.

Respiratory Effort During Sleep Apneas After Interruption of Long-term CPAP Treatment in Patients With Obstructive Sleep Apnea

Apneas generally reappear in patients with obstructive sleep apnea (OSA) when treatment with continuous positive airway pressure (CPAP) is interrupted. However, a single-night treatment interruption may be associated with a lesser severity of sleep apneas than before treatment. We hypothesized that this decrease in severity of sleep apneas reflects changes in the respiratory response to upper airway obstruction. Therefore, we compared indexes of respiratory effort during sleep in 25 patients with OSA before and after 1 year of CPAP treatment. Respiratory effort was assessed by means of an esophageal balloon. After 1 year of CPAP treatment, there was a decrease in the maximal end-apneic esophageal pressure swings (Pes) (from 56.7 +/- 5.4 to 30.3 +/- 2.6 cm H2O; p = 0.000; mean +/- SEM), in the overall increase in Pes during an apnea (35.2 +/- 3.6 vs 16.5 +/- 1.5 cm H2O; p = 0.000), as well as the rate of increase in Pes (1.1 +/- 0.1 vs 0.6 +/- 0.1 cm H2O/s; p = 0.000). Although body mass index (BMI) did not change significantly, the individual changes in BMI significantly correlated with the changes in respiratory effort after 1 year of CPAP treatment. Apnea duration and apnea-related oxygen desaturation also decreased significantly. We conclude that long-term CPAP treatment induces changes in respiratory control that persist at least on the first night of treatment interruption.

Respiratory Effort: A Factor Contributing to Sleep Propensity in Patients With Obstructive Sleep Apnea

To test the hypothesis that respiratory effort during obstructive apneas contributes, together with hypoxemia and sleep fragmentation, to excessive daytime sleepiness, we investigated the relationship between daytime sleepiness and polysomnographic variables in 44 patients with obstructive sleep apnea (OSA). In all patients, daytime sleep propensity was assessed by an 11-item standardized self-questionnaire yielding a sleepiness score and by a modified sleep latency test yielding a mean sleep latency. Respiratory effort during apneas was evaluated by measuring esophageal pressure swings using an esophageal balloon. Within each apneic cycle, we measured the esophageal pressure swings during the first three and the last three occluded efforts during the apnea to define the overall increase, its ratio to apnea duration, and the maximal effort developed during obstruction. In the group of patients as a whole, the sleepiness score was negatively correlated with the mean sleep latency (r=-0.38, p=0.01). The sleepiness score was correlated with the indexes of respiratory effort during apneas (ie, the overall increase, its ratio to apnea duration, and the maximal end-apneic swing in esophageal pressure) and with the apnea+hypopnea index. The mean sleep latency was correlated with all indexes of nocturnal hypoxemia (ie, the mean lowest oxyhemoglobin saturation [SaO2] and the index of apnea associated with a fall in SaO2 below 90% and 80%). We conclude that the degree of respiratory effort during obstructive apneas contributes to self-rated sleep propensity in patients with OSA.