Levels Of Arterial Partial Pressure Research Articles

The efficacy and safety of combined therapy with endobronchial tamponade and bronchial artery embolization for massive hemoptysis

BackgroundMassive hemoptysis is characterized by its life-threatening nature, potentially leading to airway obstruction and asphyxia. The objective of this study was to evaluate the clinical effectiveness of combining endobronchial tamponade with bronchial artery embolization (BAE) in the treatment of massive hemoptysis.MethodsBetween March 2018 and March 2022, a total of 67 patients with massive hemoptysis who underwent BAE were divided into two groups: the combination group (n = 26) and the BAE group (n = 41). Technical and clinical success rates were assessed, and adverse events were monitored following the treatment. Blood gas analysis and coagulation function indicators were collected before and after the treatment, and recurrence and survival rates were recorded during the follow-up period.ResultsAll patients achieved technical success. There were no significant differences in the clinical success rate, recurrence rates at 3 and 6 months, and mortality rates at 3 months, 6 months, and 1 year between the combination group and the BAE group. However, the hemoptysis recurrence rate at 1 year was significantly lower in the combination group compared to the BAE group (15.4% vs. 39.0%, P = 0.039). No serious adverse events were reported in either group. After treatment, the combination group showed higher levels of arterial partial pressure of oxygen (PaO2), oxygenation index (PaO2/FiO2), fibrinogen (FIB), and D-dimer (D-D) compared to the BAE group (P < 0.05). Multivariate regression analysis demonstrated a significant correlation between combined therapy and hemoptysis-free survival.ConclusionCombination therapy, compared to embolization alone, exhibits superior efficacy in improving respiratory function, correcting hypoxia, stopping bleeding, and preventing recurrence. It is considered an effective and safe treatment for massive hemoptysis.

Impact of Hypo- and Hyper-capnia on Spreading Depolarizations in Rat Cerebral Cortex.

Patients with traumatic brain injury are typically maintained at low-normal levels of arterial partial pressure of carbon dioxide (PaCO2) to counteract the risk of elevated intracranial pressure during intensive care. However, several studies suggest that management at hypercarbic levels may have therapeutic benefit. Here we examined the impact of CO2 levels on spreading depolarizations (SD), a mechanism and marker of acute lesion development in stroke and brain trauma. In an acute preparation of mechanically ventilated (30/70 O2/N2) female rats, SDs were evoked by cortical KCl application and monitored by electrophysiology and laser doppler flowmetry; CO2 levels were adjusted by ventilator settings and supplemental CO2. During 90min of KCl application, rats were maintained at hypocapnia (end-tidal CO2 22±2mmHg) or hypercapnia (57±4mmHg) but did not differ significantly in arterial pH (7.31±0.10 vs. 7.22±0.08, p=0.31) or other variables. Surprisingly, there was no difference between groups in the number of SDs recorded (10.7±4.2 vs. 11.7±3.1; n=3 rats/group; p=0.75) nor in SD durations (64±27 vs. 69±37 sec, p=0.54). In separate experiments (n=3), hypoxia was induced by decreasing inhaled O2 to 10% and single SDs were induced under interleaved conditions of hypo-, normo-, and hypercapnia. No differences in SD duration were observed. In both normoxia and hypoxia experiments, however, mean arterial pressures were negatively correlated with SD durations (normoxia R2=-0.29; hypoxia R2=-0.61, p's<0.001). Our results suggest that any therapeutic benefit of elevated CO2 therapy may be dependent on an acidic shift in pH or may only be observed in conditions of focal brain injury.

Application effects of feedforward control theory in the rollover bed treatment of mass patients with burn-explosion combined injury

Objective: To explore the application effects of feedforward control theory in the rollover bed treatment of mass patients with burn-explosion combined injury. Methods: A retrospective observational research was conducted. From June 13 to 14, 2020, 15 patients with severe burn-explosion combined injury caused by liquefied natural gas tank car explosion and conforming to the inclusion criteria were admitted to the Second Affiliated Hospital of Zhejiang University School of Medicine. There were 13 males and 2 females, aged 33-92 (66±17) years. All the patients were treated with rollover bed from 48 h post admission, and the feedforward control theory was introduced, including establishing a special feedforward control management team for rollover bed, clarifying the duties of the medical staff in the rollover bed treatment of patients, implementing the cooperation strategy of multidisciplinary physician, training and examining for 80 nurses in the temporarily organized nurse team in the form of "rollover bed workshop", and formulating the checklist and valuation list of rollover bed treatment for continuous quality control. The frequency and the total number of turning over, and successful rate of one-time posture change with the rollover bed of patients within 30 days of admission were recorded, the occurrences of adverse events caused by improper operation for the rollover bed during the treatment were observed, including respiratory and cardiac arrests, treatment interruption, unplanned extubation, bed falling, and skin graft displacement. The lowest levels of arterial partial pressure of oxygen (PaO2) and arterial partial pressure of carbon dioxide (PaCO2), the number of patients with oxygenation index>300 mmHg (1 mmHg=0.133 kPa), and the occurrence of acute respiratory distress syndrome (ARDS) of patients within 2 days of admission and on the 30th day of admission were recorded. Results: Within 30 days of admission, the patients were turned over with the rollover bed for 2 to 6 times each day, with a total of 1 320 turning over operations, the successful rate of one-time posture change reached 99.9% (1 319/1 320), and no adverse event occurred. Within 2 days of admission, the lowest levels of PaO2 and PaCO2 of the patients were (100±19) and (42±4) mmHg, respectively, and the number of patients with mild, moderate, and severe ARDS were 10, 2, and 3, respectively, and none of the patients had oxygenation index>300 mmHg. On the 30th day of admission, the lowest levels of PaO2 and PaCO2 of the patients were (135±28) and (37±8) mmHg, respectively, 3 patients developed moderate ARDS, 1 patient developed severe ARDS, and 11 patients had oxygenation index>300 mmHg. Conclusions: The introduction of feedforward control theory in the treatment of rollover bed of mass patients with burn-explosion combined injury can ensure safe and successful completion of turning over with the rollover bed, promote the repair of burn wound, and improve respiratory function, and therefore improve the treatment quality of patients.

Modeling acid-base balance for in-series extracorporeal carbon dioxide removal and continuous venovenous hemofiltration devices.

Patients with acute respiratory distress syndrome and acute kidney injury (AKI) treated by kidney replacement therapy may also require treatment with extracorporeal carbon dioxide removal (ECCO2 R) devices to permit protective or ultraprotective mechanical ventilation. We developed a mathematical model of acid-base balance during extracorporeal therapy using ECCO2 R and continuous venovenous hemofiltration (CVVH) devices applied in series for the treatment of mechanically ventilated AKI patients. Published data from clinical studies of mechanically ventilated AKI patients treated by CVVH at known infusion rates of substitution fluid without ECCO2 R were used to adjust the model parameters to fit plasma levels of arterial partial pressure of carbon dioxide (PaCO2 ), arterial plasma bicarbonate concentration ([HCO3 ]), and plasma pH (as well as certain other unmeasured physiological variables). The effects of applying ECCO2 R at an unchanged and a reduced tidal volume on PaCO2 , [HCO3 ] and plasma pH were then simulated assuming carbon dioxide removal rates from the ECCO2 R device measured in the clinical studies. Agreement of such model predictions with clinical data was good whether the ECCO2 R device was positioned proximal or distal to the CVVH device in the extracorporeal circuit. Although carbon dioxide removal rates from the ECCO2 R device measured in one previous clinical study were higher when it was placed proximal to the CVVH device, suggesting that such in-series positioning was optimal, the current mathematical model demonstrates that proximal positioning of the ECCO2 R device also results in lower bicarbonate (and, therefore, total carbon dioxide) removal from the distal CVVH device. Thus, the removal of total carbon dioxide by such extracorporeal circuits is relatively independent of the position of the in-series devices. It is concluded that the described mathematical model has quantitative accuracy; these results suggest that the overall acid-base balance when using ECCO2 R and CVVH devices in a single extracorporeal circuit will be similar, independent of their in-series position.

Impact of inspiratory muscle training on diaphragmatic mobility and arterial blood gases in patients undergoing haemodialysis

Background/aims Impairment of respiratory muscle function is common in patients with chronic kidney disease undergoing haemodialysis, and is manifested by decreased oxygenation and physical function. The purpose of this study was to analyse the impact of training with incentive spirometer on mobility of the diaphragm, arterial blood gases and functional capacity in patients with chronic kidney disease undergoing haemodialysis. Methods A pre–post research design was implemented. A total of 30 patients undergoing haemodialysis for chronic kidney disease received incentive spirometer training intradialysis three sessions a week for 8 weeks. Outcome measures were the amount of diaphragmatic mobility measured by ultrasonography, the levels of arterial partial pressure of oxygen, arterial partial pressure of carbon dioxide, oxygen saturation percentages and the distance walked in 6 minutes. Results Significant improvement from pre-treatment to post-treatment measurements occurred in all outcome measures, with P&lt;0.05. Conclusions Incentive spirometer training should be recommended to be a part of daily routine of patients with chronic kidney disease who are undergoing haemodialysis to decrease respiratory and physical function impairments.

Oxygen therapy for pulmonary arterial hypertension: We need to rethink and investigate.

Oxygen therapy for pulmonary arterial hypertension: We need to rethink and investigate.

Efficacy of Whole-Lung Lavage in Treatment of Pulmonary Alveolar Proteinosis.

The aim of the study was to investigate the therapeutic effect of whole-lung lavage (WLL) for pulmonary alveolar proteinosis (PAP). The cohort studies that investigated the therapeutic effect of WLL for PAP were selected strictly on the basis of the inclusion and exclusion criteria. The statistical analysis was performed using STATA statistical software (version 12.0; Stata Corporation, College Station, TX). Twelve studies were included in this meta-analysis. Totally, 206 PAP patients who received WLL were recruited in the 12 studies. We compared the differences in blood gas analysis and lung function before and after the treatment in this meta-analysis. The results indicated that there were statistical differences in the levels of diffusing capacity for carbon monoxide, forced expiratory volume in 1 second, forced vital capacity, and arterial partial pressure of oxygen after the treatment of WLL for patients with PAP, whereas there were no evident differences in the levels of arterial partial pressure of carbon dioxide and arterial oxygen saturation. In conclusion, WLL can evidently improve the diffusing capacity for carbon monoxide, forced expiratory volume in 1 second, forced vital capacity, and arterial partial pressure of oxygen of patients with PAP, thus WLL may be an important treatment of PAP.

Effectiveness and safety of inhaled granulocyte-macrophage colony-stimulating factor therapy in idiopathic pulmonary alveolar proteinosis

To investigate the effectiveness and safety of inhaled granulocyte-macrophage colony-stimulating factor (GM-CSF) therapy in idiopathic pulmonary alveolar proteinosis (PAP). Ten PAP patients were enrolled, who were hospitalized in the Affiliated Drum Tower Hospital of Nanjing University Medical School from January 2012 to January 2014.All the patients were treated with inhaled GM-CSF therapy, high-dose therapy for 12 weeks, GM-CSF 150 µg twice a day on days 1-7, none for days 8-14, 6 cycles, low-dose therapy for 12 weeks, GM-CSF 150 µg inhaled once a day on days 1-7, none for days 8-14, 6 cycles, and followed-up for one year. Physiologic, serologic and radiologic features of the patients were analyzed. After inhaled therapy, clinical symptoms, oxygenation indexes, pulmonary function of nine patients were improved, and high resolution CT (HRCT) showed ground-glass lesions reduced. After inhaled therapy for 6 months, the average level of arterial oxygen partial pressure (PaO₂) was significantly higher than that before therapy ((75.5 ± 7.0) vs (63.6 ± 8.9) mmHg (1 mmHg=0.133 kPa)), while alveolar-arterial oxygen pressure difference (P(A-a)O₂) was lower than before ((25.1 ± 7.1) vs (41.2 ± 13.5) mmHg) (both P<0.01). Similarly, vital capacity (VC)% predicted, forced vital capacity (FVC)% predicted and carbon monoxide diffusing capacity (DLCO)% predicted all improved after therapy ((77.3 ± 16.6)% vs (63.3 ± 16.6)%), (79.5 ± 17.6)% vs (64.9 ± 17.1)%), (69.4 ± 23.0)% vs (50.0 ± 19.9)%) (all P<0.01). The score of HRCT reduced after therapy for six months (P<0.05). While the levels of serum lactate dehydrogenase (LDH), carcinoembryonic antigen (CEA), CYFRA211 were unchanged. No serious adverse events occurred during observation. Inhaled GM-CSF therapy is safe and effective.

Effect of lung-protective ventilation with lower tidal volumes on clinical outcomes among patients undergoing surgery: a meta-analysis of randomized controlled trials.

In anesthetized patients undergoing surgery, the role of lung-protective ventilation with lower tidal volumes is unclear. We performed a meta-analysis of randomized controlled trials (RCTs) to evaluate the effect of this ventilation strategy on postoperative outcomes. We searched electronic databases from inception through September 2014. We included RCTs that compared protective ventilation with lower tidal volumes and conventional ventilation with higher tidal volumes in anesthetized adults undergoing surgery. We pooled outcomes using a random-effects model. The primary outcome measures were lung injury and pulmonary infection. We included 19 trials (n=1348). Compared with patients in the control group, those who received lung-protective ventilation had a decreased risk of lung injury (risk ratio [RR] 0.36, 95% confidence interval [CI] 0.17 to 0.78; I2=0%) and pulmonary infection (RR 0.46, 95% CI 0.26 to 0.83; I2=8%), and higher levels of arterial partial pressure of carbon dioxide (standardized mean difference 0.47, 95% CI 0.18 to 0.75; I2=65%). No significant differences were observed between the patient groups in atelectasis, mortality, length of hospital stay, length of stay in the intensive care unit or the ratio of arterial partial pressure of oxygen to fraction of inspired oxygen. Anesthetized patients who received ventilation with lower tidal volumes during surgery had a lower risk of lung injury and pulmonary infection than those given conventional ventilation with higher tidal volumes. Implementation of a lung-protective ventilation strategy with lower tidal volumes may lower the incidence of these outcomes.

Xuebijing combined with corticosteroid injection treating paraquat poisoning analysis of 146 cases

Objective To evaluate the efficacy and safety of Xuebijing combined with corticosteroid injection treating paraquat poisoning with regression analysis. Methods 146 patients of paraquat poisoning in 3 years were divided into two groups: control group and therapeutic group. 50 patients in the control group were treated with Methylprednisolone, while 96 patients in the therapeutic group were treated with Xuebijing injection (300～400 ml/d, intravenous drip) and Methylprednisolone. The patients' clinical symptoms, signs and the levels of white blood cell (WBC), Neutrophils (N), C-reactive protein (CRP), glutamic-pyruvic transaminase (ALT), aspartate aminotransferase (AST), serum creatinine (Scr) and arterial partial pressure of oxygen were collected. And patients did chest CT examinations every three days. All the data were compared between the two groups. Results ① The biochemical indicators of the control group in the 14th day [WBC,N,CRP, and PaO2 is (16.49±4.30), (84.22±21.07), (24.58±7.06), and (83.20±22.95) respectively]were better than those in the third day[WBC, N, CRP, and PaO2 is (19.21 ±5.34), (85.04± 12.33), (27.98±6.51), and (73.42±11.43)respectively], but there was not significant difference between them(P>0.05). While the biochemical indicators of the therapeutic group in the 14th day [WBC,N, CRP, and PaO2 is (9.16 ± 3.23 ), (70.48 ± 10.79), ( 17.48 ± 4.7), and (95.04± 11.93) respectively] were much better than those in the third day [WBC,N,CRP, and PaO2 is (16.96±9.95),(84.82±9.34), (27.34± 10.03), and (89.12±9.47) respectively], and there was significant difference between them( P< 0.05 ). ② The survival rate in the control group was 32% comparing to 67.71% in the therapeutic group, showing significant difference between the two group (x2=9.588, P<0.05) . ③ The patients' chest CT examinations in the therapeutic group were better than those in the control group. Conclusion Xuebijing injection combined with methylprednisolone had good effects m treating paraquat poisoning. Key words: Paraquat; poisoning, Xuebijing; Methylprednisolone; Integrative medicine

How to assess the dangers of hyperoxemia: methodological issues

We read with interest the paper by Bellomo and colleagues [1] in the previous issue of Critical Care. We agree with the authors’ fi nal conclusion that there should not be a deliberate policy to decrease the fraction of inspired oxygen (FiO 2 ) in the absence of accurate and reliable oximetry. In the developed world, accurate and reliable oximetry and blood gas results are ubiquitous in ICU settings, the context of their study. However, we have issues with the methods used to come to the conclusion that hyperoxaemia has only a weak relationship with mortality. If one wishes to show no association of hyperoxemia with outcomes, the best approach is to pick the lowest level of arterial partial pressure of oxygen (PaO 2 ). By analogy, if one wished to assess the risk of speeding prior to traffi c accidents, one would not look at the lowest speed or the speed at impact; one would, ideally, look at peak speed or average speed. Kilgannon and colleagues [2] used the fi rst blood gas measurement in the ICU and found that hyperoxemia (PaO 2 of at least 300 mm Hg) was associated with increased risk of death in the hospital. de Jonge and colleagues [3] looked at mean PaO 2 of mechanically ventilated patients in the fi rst 24 hours in ICUs and also reported an increased risk of death in patients with hyperoxemia. We are also concerned that the conclusion of the study relates to hyperoxemia when defi ned as a PaO 2 of greater than 400 mm Hg whereas the study objective was to analyze the risk of death if the PaO 2 was at least 300 mm Hg. We understand that the authors did fi nd excess mortality in their intended study group (and in those with a PaO 2 of greater than 200 mm Hg) even after adjust ment for illness severity. We are concerned that their negative conclusion is based on a diff erent (and smaller) post hoc subset of patients with a PaO 2 of greater than 400 mm Hg. By contrast, Kilgannon and colleagues [4] re-analyzed their data and reported a clear dose response with lowest hospital mortality in the PaO 2 range of 60 to 99 mm Hg and they reported a 24% increase in mortality risk for every 100 mm Hg increase in PaO 2 .

Study on hypoxemia during sleep in patients with chronic obstructive pulmonary disease

To investigate the influence of hypoxemia during sleep on elements of polysomnography (PSG) in patients with chronic obstructive pulmonary disease (COPD) and the correlation of sleep hypoxemia and arterial blood gases, pulmonary function in daytime. Two hundred and four moderate to very severe stable COPD patients with an age range of 40-75 years [mean age was (70.41+/-7.84) years ] were admitted. All patients underwent overnight PSG, and percentage of the time with oxygen saturation below 0.90 and total sleep time (T90)>or=5% was taken as nocturnal oxygen desaturation (NOD), and if not, they were non-NOD. Arterial blood gases, lung function and PSG examinations were performed in all patients. Ninety-five patients (46.57%) had NOD were enrolled. Compared with patients of non-NOD, both daytime oxygen saturation (SaO2, 0.90+/-0.04 vs. 0.94+/-0.01) and nocturnal mean SaO2 (MSaO2, 0.83+/-0.08 vs. 0.93+/-0.02) in NOD were lower significantly (both P<0.01). Sleep-related elements such as awake period (minutes: 97.86+/-41.74 vs. 76.13+/-55.15), awake frequency (times: 31.50+/-15.69 vs. 23.23+/-19.81), mean heart rate (beat per min: 80.80+/-12.80 vs. 66.21+/-6.53), sleep components [(S1+S2)%: (74.36+/-16.52)% vs. (67.55+/-12.62)%, (S3+S4)%: (12.99+/-12.18)% vs. (19.35+/-12.71)%] in NOD were significantly different from non-NOD (all P<0.01). The levels of arterial partial pressure of carbon dioxide (PaCO2), arterial partial pressure of oxygen (PaO2), percentage of forced expiratory volume in one second (FEV1) and anticipate value, percentage of forced vital capacity (FVC) and anticipate value, percentage of FEV1/FVC and anticipate value in daytime were respectively correlated with the T90, MSaO2 and minimum SaO2 (miniSaO2) in sleep. Among these measurements, PaCO2 was best correlated with sleep hypoxemia (r1=0.767, r2=-0.758, r3=-0.689, all P<0.01). Sleep hypoxemia existed generally in patients with moderate to very severe stable COPD. There was significant difference in nocturnal SaO2, daytime SaO2 and sleep-related elements between NOD and non-NOD. The measurements in daytime are correlated with sleep hypoxemia, and some of them may predict sleep hypoxemia.

Effect of radix paeoniae rubra on expressions of p38MAPK,NF-κB and iNOS in a rat model of li-popolysaccharide-induced acute lung injury

Objective To investigate the effect of radix paeoniae rubra (RPR) on expressions of p38MAPK, NF-κB and iNOS in ltpopolysaccharide (LPS)-induced acute lung injury (ALI) and explore its protective mechanism. Methods Forty Wistar rats with ALI were divided randomly into five groups: saline control group (Group A) , LPS group (Group B), RPR for treatment group (Group C), RPR for prevention group (Group D) and SB203580 group (Group E). The effects of RPR on protein content and the ratio of neutrophiles in bronchoalveolar lavage fluid (BALF), contents of malondidehyde (MDA) and serum NO in lung tissue were observed. Arterial blood was collected for blood gas analysis. Expressions of p38MAPK, NF-κB and iNOS in rat lung tissues were detected. Results Compared with Group A, expressions of p38MAPK, NF-κB and iNOS were significantly increased (P <0.01 orP< 0.05) , the protein content and the ratio of neutrophiles in BALF, contents of MDA and serum NO were significantly higher (P<0.01 or P<0.05) in Groups B, C, D and E. There was a significant decrease in the level of arterial bicarbonate and partial pressure of oxygen in Groups B, C, D and E (P<0.01 or P<0.05). Compared with Group B, the expressions of p38MAPK, NF-κB and iNOS were significantly lower, and the protein content and the ratio of neutrophiles in BALF, contents of MDA and serum NO were significantly decreased, while the levels of arterial bicarbonate and partial pressure of oxygen were significantly higher in Groups C, D and E (P<0.05 or P<0.01). Compared with Group B, the lunginjury of Groups C, D and E was significantly alleviated, while there was no statistical difference among Groups C, D and E in the indices of lung injury. Conclusion Protective effect of RPR on LPS-induced ALI is closely related to the inhibited expressions of p38MAPK, NF-κB and iNOS. Key words: Radix Paeoniae Rubra; Respiratory distress syndrome, adult; Lipopolysaccha-ride; Mitogen-activated protein kinases; NF-kappa B

Permissive hypercapnia to decrease lung injury in ventilated preterm neonates

Lung injury in ventilated premature infants occurs primarily through the mechanism of volutrauma, often due to the combination of high tidal volumes in association with a high end-inspiratory volume and occasionally end-expiratory alveolar collapse. Tolerating a higher level of arterial partial pressure of carbon dioxide (PaCO2) is considered as 'permissive hypercapnia' and when combined with the use of low tidal volumes may reduce volutrauma and lead to improved pulmonary outcomes. Permissive hypercapnia may also protect against hypocapnia-induced brain hypoperfusion and subsequent periventricular leukomalacia. However, extreme hypercapnia may be associated with an increased risk of intracranial hemorrhage. It may therefore be important to avoid large fluctuations in PaCO2 values. Recent randomized clinical trials in preterm infants have demonstrated that mild permissive hypercapnia is safe, but clinical benefits are modest. The optimal PaCO2 goal in clinical practice has not been determined, and the available evidence does not currently support a general recommendation for permissive hypercapnia in preterm infants.

Interaction of chemoreceptor effects and its dependence on the intensity of stimuli.

We have studied the way in which carotid and medullary chemoreceptor effects combine to control respiration in pentobarbital anesthetized dogs. The carotid sinuses were autoperfused from a membrane oxygenator system to produce either normoxic or hypoxic-hypercapnic blood without producing brain stem hypoxia. The dogs breathed CO2 in O2, N2 mixtures regulated to produce isocapnic levels of arterial partial pressure of CO2 (PaCO2) of 36, 54, and 68 Torr at PaO2 = 87. Tidal volume (VT) increased (P less than 0.05) from a control value of 317 ml to 545 at PaCO2 = 54 but did not increase further at PaCO2 = 68. Carotid chemoreceptor stimulation increased VT to 432 ml at PaCO2 = 36 (P less than 0.05) but did not increase VT at the higher levels of PaCO2. Thus, VT has reached a maximum at PaCO2 = 54 Torr and was not increased further by either chemoreceptor drive. Breathing frequency (f) increased (P less than 0.05) from an eupnic value of 20.2 breaths/min to 35.5 and 41.3 at PaCO2 = 54 and 68, respectively. Carotid chemoreceptor stimulation increased (P less than 0.05) f by 7.7, 5.2, and 5.0 breaths/min at each of the levels of PaCO2. Tidal volume exhibited a less-than-additive (P less than 0.05) combination of chemoreceptor effects but f was not significantly different from additive. We conclude that, in pentobarbital-anesthetized dogs, f continues to increase at chemoreceptor drives beyond those at which VT reaches a maximum. This VT nonlinearity may be responsible for the different interactions found in these experiments.