Total Respiratory Time Research Articles

Metabolic and ventilatory changes during postural change from the supine position to the reclining position in bedridden older patients.

The prevention of pneumonia in bedridden older patients is important, and its recurrence in these patients is a relevant issue. Patients who are bedridden and inactive, and have dysphagia are considered to be at risk for pneumonia. Efforts to reduce the bedridden state and low activity may be necessary to reduce the risk of developing pneumonia in bedridden older patients. This study aimed to clarify the effects of postural change from the supine position to the reclining position on metabolic and ventilatory parameters and on safety in bedridden older patients. Using a breath gas analyzer and other tools, we assessed the following 3 positions: lying on the back (supine), resting in the Fowler position (Fowler), and resting in an 80° recline wheelchair (80°). Measurements were oxygen uptake, carbon dioxide output, gas exchange ratio, tidal volume (VT), minute volume, respiratory rate, inspiratory time, expiratory time, total respiratory time, mean inspiratory flow, metabolic equivalents, end-expiratory oxygen, and end-expiratory carbon dioxide as well as various vital signs. The study analysis included 19 bedridden participants. The change in oxygen uptake driven by changing the posture from the supine position to the Fowler position was as small as 10.8 mL/minute. VT significantly increased from the supine position (398.4 ± 111.2 mL) to the Fowler position (426.9 ± 106.8 mL) (P = .037) and then showed a decreasing trend in the 80° position (416.8 ± 92.5 mL). For bedridden older patients, sitting in a wheelchair is a very low-impact physical activity, similar to that in normal people. The VT of bedridden older patients was maximal in the Fowler position, and the ventilatory volume did not increase with an increasing reclining angle, unlike that in normal people. These findings suggest that appropriate reclining postures in clinical situations can promote an increase in the ventilatory rate in bedridden older patients.

Effects of Inspiratory Load on Chest Wall Kinematics, Breathing Pattern, and Respiratory Muscle Activity of Mouth-Breathing Children.

We sought to evaluate the acute effects of different inspiratory loads using nasal and oral interfaces on the volumes of the chest wall and its compartments, breathing pattern, and respiratory muscle activation in children with mouth-breathing syndrome. Children with mouth-breathing syndrome were randomized into 2 groups, one with an inspiratory load intensity 20% of maximum inspiratory pressure (n = 14), and the other with an inspiratory load intensity 40% of maximum inspiratory pressure (n = 15). The chest wall volumes and electromyography of sternocleidomastoid, rectus abdominis, scalene, and internal intercostal muscles were used to analyze respiration against the 2 load intensities and using 2 interfaces (ie, nasal and oral). A total of 72 children with mouth-breathing syndrome were recruited, and 29 were evaluated in this study. The use of inspiratory load promoted improvement in the components of the breathing pattern: breathing frequency (P = .039), inspiratory time (P = .03), and total respiratory time (P = .043); and increases in tidal volume (P < .001), end-inspiratory volume (P < .001), and electrical activity of scalene muscles and sternocleidomastoid muscles (P < .001) when compared to quiet breathing. The load imposed via a nasal interface versus an oral interface provided an increase in tidal volume (P = .030), end-inspiratory volume (P = .02), and electrical activity of scalene muscles (P < .001) and sternocleidomastoid muscles (P = .02). The use of acute inspiratory loads improved the breathing pattern and increased lung volume and electrical activity of inspiratory muscles. This work brings new perspective to the investigation of using nasal interfaces during the application of inspiratory loads. The nasal interface was more effective compared to the oral interface commonly used in clinical practice.

Effects of Breathing Exercises in Patients With Chronic Obstructive Pulmonary Disease: Systematic Review and Meta-Analysis.

ObjectiveTo update evidence on the effects of breathing exercises (BEs) on ventilation, exercise capacity, dyspnea, and quality of life (QoL) in chronic obstructive pulmonary disease (COPD) patients.MethodsRandomized controlled trials investigating the effects of BEs in COPD patients published through May 2018, were retrieved from five electronic databases (MEDLINE, CINAHL, Cochrane, Scopus, and ScienceDirect). Risk of bias and quality of evidence were assessed, using Cochrane Collaboration’s tool, and the Grading of Recommendation Assessment, Development, and Evaluation (GRADE) approach, respectively.ResultsNineteen studies (n=745), were included. Quality of evidence, was low to moderate. When compared to the control groups, respiratory rate significantly (p≤0.001) improved in the pursed-lip breathing (PLB), ventilatory feedback (VF) plus exercise, diaphragmatic breathing exercise (DBE), and combined BEs. Additionally, PLB significantly improved tidal volume (p<0.001), inspiratory time (p=0.007), and total respiratory time (p<0.001). VF plus exercise significantly improved inspiratory capacity (p<0.001), and singing significantly improved the physical component of QoL, than did the control groups (p<0.001). All BEs did not significantly improve dyspnea, compared to the controls (p>0.05).ConclusionPLB, VF plus exercise, DBE, combined BEs, and singing could be used to improve ventilation and QoL. Based on low to moderate quality of evidence, use of these BEs to improve ventilation and QoL in COPD patients is conditional (Registration No. CRD42018102995).

Respiratory Function in Healthy Taiwanese Infants: Tidal Breathing Analysis, Passive Mechanics, and Tidal Forced Expiration.

BackgroundAlthough infant lung function (ILF) testing is widely practiced in developed Western countries it is not typically performed in Eastern countries, and lung measurements are scarce for Asian infants. Therefore, this study aimed to establish normal reference values for Taiwanese infants.Materials and MethodsFull-term infants without any chronic diseases and major anomalies were enrolled in the Prediction of Allergies in Taiwanese Children (PATCH) cohort study. Detailed medical data, such as body weight and length, birth history, and histories of previous illness and hospitalization were recorded. Lung function measurements such as analysis of tidal breathing, passive respiratory mechanics, and forced tidal expiratory flow-volume curves were obtained through Jaeger Masterscreen BabyBody Paediatrics System. Multiple linear analyses were performed to determine various parameters of the lung function tests.ResultsILF test parameters were collected from 126 infants, and 189 tests were performed. The results revealed that the ratio of time to peak expiratory flow to total expiratory time, the ratio of volume to peak expiratory flow to total expiratory volume, and the ratio of inspiratory time to total respiratory time remained relatively constant despite differences in age. However, body length is the strongest independent variable influencing tidal volume, respiratory rate, resistance, compliance, and maximal expiratory flow at functional residual capacity.ConclusionAccording to our review of relevant literature, this is the first study to establish a reference data of ILF tests in the Asian population. This study provided reference values and regression equations for several variables of lung function measurements in healthy infants aged less than 2 years. With these race-specific reference data, ILF can more precisely and efficiently diagnose respiratory diseases in infants of Chinese ethnicity.

Electrically stimulated ventilation feedback improves the ventilation pattern in patients with COPD.

[Purpose] We aimed to determine the effects of ventilation feedback using electrical stimulation on ventilation pattern during exercise in patients with chronic obstructive pulmonary disease (COPD), and develop new rehabilitation methods. [Subjects] This randomized double-blind placebo-controlled trial included 24 patients with COPD. [Methods] Phasic electrical stimulation during expiration (PESE) or a placebo was given to all the cases. Minute ventilation (VE), tidal volume (TV), respiratory rate (RR), expiratory time (Te), total respiratory time (Ttot), dead-space gas volume to tidal gas volume (VD/VT), oxygen uptake (VO2), carbon dioxide output (VCO2), Borg scale (Borg), and percutaneous oxygen saturation (SpO2) during rest and exercise were assessed. [Results] The placebo group showed no obvious change in ventilation measurements at rest or during exercise. However, in the PESE group, TV, Te, and Ttot significantly increased, while RR and VD/VT significantly decreased during exercise compared with the baseline measurements. Borg scores, SpO2, VO2, or VCO2 did not differ significantly. [Conclusion] PESE improves the ventilation pattern during rest and exercise. Furthermore, PESE does not increase VO2, which may indicate an increased workload. Biofeedback may contribute to PESE effects. Stimulation applied during expiration may evoke sensations increasing prolonged expiration awareness, facilitating prolongation.

Response characteristics for thermal and pressure devices commonly used for monitoring nasal and oral airflow during sleep studies

We examined thermocouple and pressure cannulae responses to oral and nasal airflow using a polyester model of a human face, with patent nasal and oral orifices instrumented with a dual thermocouple (F-ONT2A, Grass) or a dual cannula (0588, Braebon) pressure transducer (±10 cm H2O, Celesco) system. Tidal airflow was generated using a dual compartment facemask with pneumotachographs (Fleisch 2) connected to the model orifices. During nasal breathing: thermocouple amplitude = 0.38 Ln [pneumotachograph amplitude] + 1.31 and pressure cannula amplitude = 0.93 [pneumotachograph amplitude]2.15; during oral breathing: thermocouple amplitude = 0.44 Ln [pneumotachograph amplitude] + 1.07 and pressure cannula amplitude = 0.33 [pneumotachograph amplitude]1.72; (all range ∼0.1–∼4.0 L s−1; r2 > 0.7). For pneumotachograph amplitudes <1 L s−1 (linear model) change in thermocouple amplitude/unit change in pneumotachograph amplitude was similar for nasal and oral airflow, whereas nasal pressure cannula amplitude/unit change in pneumotachograph amplitude was almost four times that for oral. Increasing oral orifice area from 0.33 cm2 to 2.15 cm2 increased oral thermocouple amplitude/unit change in pneumotachograph amplitude by ∼58% but decreased pressure cannula amplitude/unit change in pneumotachograph amplitude by 49%. For pneumotachograph amplitudes up to 1 L s−1, alterations in inspiratory/expiratory ratios or total respiratory time did not affect the sensitivity of either nasal or oral pressure cannulae or the nasal thermocouple, but the oral thermocouple sensitivity was influenced by respiratory cycle time. Different nasal and oral responses influence the ability of these systems to quantitatively assess nasal and oral airflow and oro-nasal airflow partitioning.

Sevoflurane and isoflurane monoanesthesia abolished the phrenic long-term facilitation in rats

Phrenic long-term facilitation (pLTF) is a form of respiratory plasticity, manifested by prolonged increase in peak amplitude of phrenic nerve activity (PNA) after episodes of acute intermittent hypoxia (AIH). The aim was to investigate the effects of sevoflurane and isoflurane monoanesthesia at equipotent anesthetic doses on the expression of amplitude pLTF. Experiments were performed on Sprague-Dawley anesthetized, vagotomized, and mechanically ventilated rats. Two experimental groups, sevoflurane and isoflurane, and a control group (urethane-anesthetized) were formed. Peak amplitude of phrenic nerve activity, respiratory frequency and breathing rhythm parameters (Ti, inspiratory duration; Te, expiratory duration; and Ttot, total respiratory time duration) were analyzed during hypoxic episodes, and at 15, 30, and 60min after the last hypoxic episode. In the control group average PNA increased by 173.03±70.16% (p<0.001), at 60min after the last hypoxic episode compared to baseline values. Therefore amplitude pLTF was induced. In the sevoflurane and isoflurane groups PNA failed to increase, and in fact decreased by 15.79±15.18% and 31.00±11.00%, respectively (p>0.05). Amplitude pLTF was abolished during sevoflurane and isoflurane monoanesthesia.

The clincal significace of pulmonary function detection in normal toddler

Objective To explore the development of pulmonary function of normal toddlers between 1 and 3 years old.Methods Totally 115 normal toddlers were divided into 2 groups according to their age,i.e,1 ～ 2 years old,2～3 years old.The indicator of small and big airway examine respiratory system static compliance,total airway resistance and functional residual volume were observed.Results No significant difference was found between male and female toddler( P ＞0.05 ).Between the two groups,the difference of respiratory rate was not significant( 27 vs 26,t =1.512,P ＞0.05 ).The values of tidal volumes in the 2 ～ 3 years group was notably higher than in the 1 ～ 2 years group(0.123 vs 0.091,t =8.586,P ＜ 0.01 ),but the values of tidal volumes per kilogram body weight was not significantly different (0.0091 vs 0.0087,t =1.958,P ＞ 0.05 ).The peak tidal expiratory flow in the elder group was similarly distinctly higher than that in the other group.The measured tidal breathing flow volume loops were both displayed uncharacteristic ellipse.The rations of inspiratory time to total respiratory time,the volume to reach peak tidal expira-tory flow to total expiratory volume,tidal expiratory flow at 25％ remaining expiration to peak expiratory flow and mid-tidal expiratory flow to mid-tidal inspiratory flow were not significantly different between two groups (P ＞ 0.05 ).Butthe ratio of peak tidal flow to tidal volume( 1.257 vs 1.095,t =2.099,P ＜ 0.05 ) and the respiratory system resistances( 2.698 vs 2.071,t =3.762,P ＜0.01 )were evidently lower in the elder group than in the younger.The respiratory system compliances(0.353 vs 0.254,t =4.296,P ＜0.01 ) and functional residual capacities(0.272 vs 0.212,t =8.469,P ＜0.01 ) were significantly higher in the elder group than that in the younger,but the values per kilogram body weight was not significantly different( P ＞0.05 ).It was shown that the values of tidal volume,peak tidal expiratory flow,respiratory system static compliance,residual volume were significantly different(0.0198 vs 0.0198,t =0.000,P ＞0.05),between two groups.The values of each parameter mentioned above were increased with age,and were positively correlated with body weight(γ=0.457,0.849,0.572,0.319 all P＜0.01 ).Conclusion Tidal breathing flow volume loop could show functions of small and large airways and partially replace the maximum expiratory flow loop.The parameters were stable in toddlers and could be used as reasonable index to evaluate the pulmonary function changes in pulmonary diseases.The ventilatory function,residual volume,respiratory system static compliance and peak tidal flow were increased with the age,which coincides with the rule of development of toddlers. Key words: Child ; Respiratory function tests

Erratic control of breathing during exercise in patients with systemic lupus erythematosus: a pilot-study

The aim of this study was to provide a comprehensive evaluation of the pattern and timing of breathing during incremental exercise in a sample of women living with systemic lupus erythematosus (SLE). In this cross-sectional study, 20 women with SLE without pulmonary involvement were compared with 20 gender-, body mass index- (BMI), and age-matched healthy individuals. By using a cardiopulmonary incremental exercise test, the following parameters were assessed: tidal volume (VT); breathing frequency (BF); total respiratory time (TOT); inspiratory time (TI); expiratory time (TE); inspiratory time to total time (TI/TOT); mean inspiratory flow (VT/TI); ventilatory equivalent for carbon dioxide (VE/VCO2) and end-tidal carbon dioxide pressure (PETCO2). BF and BF/VT were significantly higher in patients with SLE versus controls, whereas VT, TE, TI and TOT were significantly lower in the former group ( p<0.05). Additionally, patients with SLE presented higher VE/VCO2 and lower PETCO2 than controls ( p<0.05), suggesting a ventilatory inefficiency. We reported compelling evidence of abnormal pattern and timing of breathing during incremental exercise in SLE. Considering that an erratic control of breathing may play an important role in exercise intolerance and fatigue, respiratory exercises emerge as a potential treatment for these symptoms in patients with SLE.

Tidal Breathing Flow-Volume Loop Analysis for the Diagnosis and Staging of Tracheal Collapse in Dogs

Tracheoscopy is generally used for the diagnosis of tracheal collapse (TC) in dogs; yet, it is costly, requires anesthesia, and can irritate the airway. The tidal breathing flow-volume loop (TBFVL) is a safe, quick, and noninvasive pulmonary function test currently used in humans. TBFVL will differentiate dogs with TC from healthy controls and contribute to disease grading. Twenty-eight dogs with naturally occurring TC and 10 healthy controls. Cross-sectional, prospective clinical study: The 38 dogs were assigned to one of 4 groups based on tracheoscopy results: group A (n=10, healthy controls), group B (n=10, grade I TC), group C (n=10, grade II TC), and group D (n=8, grade III TC). The TBFVL measurement was performed on all dogs and loops were assessed for their shape. Forty-four TBFVL parameters were calculated. Two types of TBFVL shapes were identified: Type I, representative of the 10 healthy controls, and Type II, representative of the 28 dogs with TC. Statistical analysis showed the dogs could be differentiated into healthy or affected by TC by 3 indices, TE/TI (expiratory time divided by inspiratory time), TI/TTOT (inspiratory time divided by total respiratory time), and EF75/IF75 (expiratory flow at end tidal volume plus 75% end tidal volume divided by inspiratory flow at end tidal volume plus 75% end tidal volume). The TC could also be graded as mild-moderate (grades I and II) or severe (grade III), showing a diagnostic value of 97.4%. TBFVL is accurate, quick, noninvasive, and safe and can contribute to the diagnosis of TC in dogs.

Effect of Expiratory Positive Airway Pressure on Sleep Disordered Breathing

We sought to determine the effect of expiratory positive airway pressure on end expiratory lung volume (EELV) and sleep disordered breathing in obstructive sleep apnea patients. Observational physiology study We studied 10 OSA patients during sleep wearing a facial mask. We recorded 1 hour of NREM sleep without treatment (baseline) and 1 hour with 10 cm H2O EPAP in random order, while measuring EELV and breathing pattern. The mean EELV change between baseline and EPAP was only 13.3 mL (range 2-25 mL). Expiratory time was significantly increased with EPAP compared to baseline 2.64 +/- 0.54 vs 2.16 +/- 0.64 sec (P = 0.002). Total respiratory time was longer with EPAP than at baseline 4.44 +/- 1.47 sec vs 3.73 +/- 0.88 sec (P = 0.3), and minute ventilation was lower with EPAP vs baseline 7.9 +/- 4.17 L/min vs 9.05 +/- 2.85 L/min (P = 0.3). For baseline (no treatment) and EPAP respectively, the mean apnea+hypopnea index (AHI) was 62.6 +/- 28.7 and 56.8 +/- 30.3 events per hour (P = 0.4). In OSA patients during sleep, the application of 10 cm H2O EPAP led to prolongation of expiratory time with only marginal increases in FRC. These findings suggest important mechanisms exist to avoid hyperinflation during sleep.

Requisite for stringent control of oxygen therapy in the neonatal period

Brief administrations of oxygen are commonly given to term and premature newborns after delivery or before invasive procedures to prevent hypoxaemia. But, to date, no study has validated the usefulness and innocuity of this pre-oxygenation method. Now, in the current issue of the European Respiratory Journal , Lofaso et al. 1 report the deleterious effects of oxygen administration in newborn mice. The main message of their work is that repeated brief administration of 100% oxygen during a critical window, i.e. the first 3 days of life, was associated with a significant decrease in minute ventilation, owing to an increase in absolute total respiratory time and apnoea duration. Most importantly, these adverse effects increased with repeated exposure. The exposure to a lower concentration of oxygen (30%) produced comparable effects on breathing pattern. In both situations, recovery was observed after return to normoxia. Before analysing the clinical implications of this work, it is worth discussing the methodology of the study. It is extremely difficult to perform studies in human newborns and infants because of the multitude of ethical issues and the risks associated with unproven therapies in this vulnerable population. In addition, there is an international agreement among paediatricians on the impossibility of performing invasive or potentially dangerous studies in …

Pulmonary function at peak exercise in patients with chronic heart failure

Background Various respiratory abnormalities are associated with chronic heart failure (CHF). However, changes in inspiratory capacity (IC) and breathing pattern from rest to exercise in patients with CHF have not been thoroughly investigated in these patients. Materials and methods Seventy seven (66 male/11 female) patients with clinical stable CHF (age: 52 ± 11 years) were studied. All the patients underwent pulmonary function tests, including measurements of IC and maximal inspiratory pressure (Pimax) at rest and then a maximal cardiopulmonary exercise testing (CPET) on a treadmill. During the CPET, IC was measured every 2 min. Pimax was measured again after the end of CPET. Results Percent predicted forced expiratory volume in 1 s (FEV 1) was 91 ± 12, %predicted forced vital capacity (FVC) was 92 ± 13, %FEV 1/FVC was 81 ± 4, and %predicted IC was 85 ± 18. Peak exercise IC was lower than resting (2.4 ± 0.6 vs. 2.6 ± 0.6 l, p < 0.001). Analysis of variance between Weber's groups revealed statistically significant differences in peak exercise IC ( p < 0.001), V E/ V CO 2 slope ( p < 0.001), resting Pimax ( p = 0.005) and post-exercise Pimax( p < 0.001). At rest, there was a statistically significant difference in end-tidal CO 2 ( P etco2 ) ( p = 0.002), in breathing frequency ( p = 0.004), in inspiratory time (Ti) ( p = 0.04) and in total respiratory time ( T Tot) ( p = 0.004) among Weber's groups. At peak exercise there was a statistically significant decrease in minute ventilation ( V E) ( p < 0.001), tidal volume ( V T) ( p < 0.001), respiratory cycle ( V T/ T I) ( p < 0.001) and P etco2 ( p < 0.001). Peak IC was correlated with peak V O 2 ( r = 0.72, p < 0.001), anaerobic threshold ( r = 0.71, p < 0.001), V O 2 / t slope ( r = 0.54, p < 0.0001), and post-exercise Pimax ( r = 0.62, p < 0.001). Conclusions In patients with CHF, peak exercise IC is reduced in parallel with disease severity, which is probably due to respiratory muscle dysfunction.

Do sinusoidal models of respiration accurately reflect the respiratory events of patients breathing on nebulizers?

The amount of drug that is delivered by nebulization is a combination of the physical properties of the agent being nebulized, the performance of the nebulizer, and the pattern of breathing of the patient. To avoid biological variation, mechanical models of breathing are frequently employed during the evaluation of the performance of a device. For simplicity, many investigators use sinusoidal models of breathing to calculate the expected inhaled mass, although some use square waves and other more complex models. Most assume that the duration of inspiration (Ti) is half of the total respiratory time (Ttot). This study compared the calculated inhaled mass from which the expected pulmonary deposition was estimated from the actual pattern of breathing of 43 children with cystic fibrosis (CF) breathing from an unvented nebulizer with a low dead volume and appropriate particle size distribution with that from a sinusoidal pattern of breathing using the same tidal volume (VT) and respiratory rate. The respiratory duty cycle (Ti/Ttot) was 0.45 +/- 0.05, which meant that less time was spent during inspiration than that found in a pure sinusoidal pattern. The difference between the predicted deposition from the actual pattern of breathing and that calculated from the sinusoidal model was 12 +/- 7%, which correlated with the respiratory rate (r = 0.67, P < 0.001). The degree of lung disease did not influence the discrepancy between the two values. In general, the actual VTs and respiratory rates were less in the patients than those employed in mechanical models of pediatric breathing. Although some patients had respiratory patterns that could be represented accurately with a sinusoidal model, most did not, and there were wide variations from child to child. These results suggest that there are both systematic and random errors arising from the use of a sinusoidal waveform to mimic respiratory events in patients.

Ventilatory responses and entrainment of breathing during rowing

The purpose of this investigation was to investigate the hypothesis that respiration was coupled with the mechanics of the rowing stroke. In the first part of the study, physiologic responses during incremental exercise on the variable-resistance rowing ergometer were compared in 16 untrained female subjects (U), 17 collegiate female rowers (C), and 21 elite oarswomen (E). Minute ventilation (VE) and frequency of respiration (fR) were examined on a log scale as their relationship with oxygen consumption (VO2) was exponential. The slopes for log VE/VO2 were similar for collegiate (0.65 +/- 0.02) and elite (0.59 +/- 0.01) rowers, but the slope was significantly higher for the untrained (0.87 +/- 0.01) subjects (P less than 0.001). Elite rowers utilized a higher tidal volume (VT) response per VO2 (0.68 +/- 0.04 vs 0.30 +/- 0.05; P = 0.01) and lower log fR response per VO2 (0.27 +/- 0.02 vs 0.50 +/- 0.03; P = 0.01) compared with collegiate rowers. The ratio of fR/strokes per minute (SPM) averaged 1.5 in E athletes but varied in the U and C groups. In the second part of the study, pattern and timing of respiration were recording using an inspiratory pneumotachygraph, analyzed, and compared with specific phases of the rowing stroke in ten untrained subjects and nine elite rowers. The ratio of inspiratory time (T1)/total respiratory time (TTOT) decreased during the drive phase and increased during the recovery phase in both untrained subjects and elite rowers.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Breathing Pattern in Children with Asthma

The breathing pattern in children with asthma was studied, using respiratory inductive plethysmography. The subjects were 31 children with mild to moderate asthma (15 males, 16 females; aged 6-15 years, average 11 years). The respiratory rate was 25.5 +/- 10.7/min. (mean +/- S.D.) during asthma attacks and 18.4 +/- 5.0/min. between attacks with a significant increase during attacks (P less than 0.001). The expiratory time was 1.774 +/- 0.833 second during attacks, and 2.125 +/- 0.602 seconds between attacks. The expiratory time to total respiratory time ratio (TE/TTOT) was 0.631 +/- 0.056 during attacks and 0.608 +/- 0.035 between attacks. Thus there was a slight prolongation at the time of attack, but the difference was not significant. The tidal volume was increased slightly during mild and moderate attacks. VT/TI (mean inspiratory flow) was increased during attacks. The respiratory pattern was thoracic during attacks and changed to the abdominal pattern with improvement.

The effects of chronic airflow limitation, increased dead space, and the pattern of ventilation on gas exchange during maximal exercise in advanced cystic fibrosis.

Although exertional hypercapnea has been observed in patients with advanced cystic fibrosis (CF), the causes have not been fully elucidated. In 14 patients aged 15 to 35 yr of age with advanced CF, the effects of chronic airflow limitation (CAL), increased physiologic dead space (VD), and the timing components of ventilation (VE) on gas exchange during maximal exercise were assessed. The patients were divided into those who retained CO2 during exercise, the CO2R group, and those who did not, the CO2NR group. CO2 retention was defined as a rise in end-tidal CO2 tension of 5 mm Hg or more or to a value greater than 50 mm Hg during a progressive exercise test on a cycle ergometer. CO2 retention occurred in half the subjects, usually by the halfway mark of the test, and did not rise progressively as exercise continued. It was associated with a low VE caused by a low tidal volume (VT) that was the result of a short inspiratory time to total respiratory time ratio (0.33 +/- 0.03 versus 0.38 +/- 0.04, p less than 0.02), whereas there was no difference in mean inspiratory flow or respiratory rate. Although the CO2R group had the worst CAL, with a FEV1 of 28 +/- 7 versus 41 +/- 12% predicted (p less than 0.5) and a FVC of 42 +/- 12 versus 61 +/- 9% predicted (p less than 0.01), the VT at maximal work expressed as a percentage of FVC was lower (45 +/- 13 versus 60 +/- 11, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)