Vital Capacity Breathing Research Articles

Effects of mat Pilates training and habitual physical activity on thoracoabdominal expansion during quiet and vital capacity breathing in healthy women.

Pilates is a body/mind method that requires different types of exercise (balance, endurance, strength, and flexibility) and attention to muscle control, posture, and breathing. The aim of the present study was to investigate the effects of 12 weeks of mat Pilates training and habitual physical activity on thoracoabdominal motion of healthy and physically active women. Thirty-five women without experience in Pilates exercise, aged between 18 and 35 years, participated in the study (habitual physical activity group: N.=14; and mat Pilates group: N.=21). Three-dimensional kinematic analysis was used to evaluate total and separate thoracoabdominal compartments' expansion (superior and inferior thorax and abdomen), contribution of each compartment to total thoracoabdominal expansion, and coordination between thoracoabdominal compartments. After 12 weeks of mat Pilates training, thoracoabdominal expansion during quiet breathing was improved by increasing the expansion of abdomen by about 33% (P=0.01). Moreover, expansion of superior (P=0.04) and inferior thorax (P=0.02) and abdomen (P=0.01) was also improved in Pilates (35%, 33%, and 37%, respectively) compared to the habitual physical activity group, after the experimental protocol. Finally, the habitual physical activity group presented a decrease of 13% in the expansion of abdomen (P=0.002). The results suggest the capability of Mat Pilates in improving the action of respiratory and abdominal muscles during breathing and, thus, its benefits to breathing mechanics.

Hemodynamic Responses and intubating conditions in laryngeal mask airway insertion a comparative study of propofol versus sevoflurane

Background: LMA is an effective alternative to the endotracheal tube for securing the airway in short surgical procedures. Propofol is a widely used anaesthetic agent for the insertion of Laryngeal Mask Airway. Sevoflurane is a volatile anaesthetic agent, which combines rapid, smooth inhalational induction of anaesthesia with rapid recovery, making it ideal for day care anaesthesia. Objective: To study if the use of sevoflurane can be used as an alternative to IV propofol for laryngeal mask airway insertion. Primary objective: Hemodynamic responses during Laryngeal mask insertion. Secondary objective: Intubating conditions during laryngeal mask airway insertion. Study design: A Randomized control trial. Methods: 100 adults were allocated by randomization into two groups of 50 each; group P (Propofol) and group S (Sevoflurane). Patients in group P were induced with 2.5mg/kg intravenous propofol with 50%O2 & 50%N2O and in group S with 8% sevoflurane in 50%O2 & 50% N2O vital capacity breath technique. Laryngeal mask airway was inserted after adequate jaw relaxation was attained and hemodynamic responses like pulse rate, blood pressure were monitored. The grading of conditions for laryngeal mask airway insertion and number of attempts were noted. All the data collected was analysed statistically. Results: We observed that more number of attempts were required for LMA insertion in Group S (14.0%) compared to Group P (0.0%) which is statistically significant with P=0.012. Heart rate at one minute and 2 minutes after LMA insertion showed a fall with Propofol which was statistically significant as compared to Sevoflurane. There is a significant difference of fall in mean arterial blood pressure in group P during induction, one minute, 2 minutes and 5 minutes when compared between the two groups. Sevoflurane took longer time for induction and LMA insertion compared to Propofol which is statistically significant. Moderate patient movement were noticed in 5 patients of group S and no patient movement were noticed in group P and is statistically significant (P – 0.022). Quality of insertion with propofol was excellent in all patients. With sevoflurane quality of insertion ranged from excellent to satisfactory. Conclusion: Sevoflurane is associated with good hemodynamic stability but intubating conditions provided with propofol is superior. Prolonged time for jaw relaxation with sevoflurane when compared to propofol may delay laryngeal mask airway insertion. Quality of insertion with propofol was excellent in all patients. With sevoflurane quality of insertion ranged from excellent to satisfactory.

Comparison of intravenous induction with propofol to vital capacity breath induction with sevoflurane for insertion of laryngeal mask airway

<p class="abstract"><strong>Background:</strong> The increasing emphasis on day care anaesthesia has led to the greater use of laryngeal mask airway (LMA) as an alternative to tracheal intubation for short procedure surgeries. Satisfactory insertion of LMA after induction of anaesthesia requires sufficient depth for suppression of airway reflexes. This study was performed to compare intravenous induction with Propofol to vital capacity breath induction with sevoflurane for LMA insertion<span lang="EN-IN">. </span></p><p class="abstract"><strong>Methods:</strong> In this study 100 ASA 1 and ASA 2 patients aged between 20 and 40 years, undergoing short surgical procedures lasting 30 to 60 minutes, were included. The P group received Inj. Propofol 2.5 mg/kg IV whereas the S group received Sevoflurane 8% vital capacity breaths. After the loss of eyelash reflex, which was considered the end point of induction, the LMA insertion was attempted by an anaesthesiologist blinded to the induction technique. The data that was recorded was induction time with both the drugs, characteristics of LMA insertion, hemodynamic responses and complications if any. The number of attempts at insertion was also noted<span lang="EN-IN">.</span></p><p class="abstract"><strong>Results:</strong> Induction time was 60.1±8.98 secs for propofol induction and 72.8±15.86 for sevoflurane vital capacity breath induction which was found statistically significant. The insertion conditions were found excellent in 88% in the propofol group and 90% in the sevoflurane group which was comparable. There was no statistically significant difference found in the time or characteristics of insertion between both the groups. No incidence of complications was found in both groups<span lang="EN-IN">. </span></p><p class="abstract"><strong>Conclusions:</strong> Induction with sevoflurane vital capacity breath inhalation compared equally with induction with intravenous propofol for LMA insertion in patients undergoing short surgical procedures.</p>

Comparison of sevoflurane and propofol for laryngeal mask airway insertion and pressor response in patients undergoing gynecological procedures.

Background and Aims:A popular method of providing anesthesia for laryngeal mask airway (LMA) insertion is with the use of propofol. However, bolus propofol has been associated with adverse effects such as hypotension, apnea and pain on injection. Hence, time is needed to search an alternative. We aimed to compare the induction characteristics, ease of LMA insertion, hemodynamic changes and complications with inhalation of 8% sevoflurane vital capacity breath and propofol.Material and Methods:A prospective randomized study of 60 American Society of Anesthesiologists' Grade I and II patients was conducted and distributed among two groups with 30 each undergoing gynecological procedures under general anesthesia. Group P received the injection propofol and Group S received sevoflurane. At the end point of induction, the LMA insertion was attempted. Scoring systems were used to grade the conditions for insertion of the LMA. Induction, LMA insertion characteristics, hemodynamic changes, complications were assessed. Data were recorded and analyzed. Comparison among the study groups was done with unpaired t-test, Mann–Whitney test and Chi-square test.Results:Sevoflurane took a longer time for induction and for LMA insertion than propofol. There was no statistically significant difference between the two groups, with respect to LMA insertion characteristics, heart rate, mean arterial pressure. It is concluded that sevoflurane is associated with good hemodynamic stability and may prove useful incases where propofol is to be avoided. However, the ease of insertion provided with propofol is better.

Respiratory dynamics in phonation and breathing—A real-time MRI study

The respiratory system is a central part of voice production, but for phonation neither the underlying functional relations between diaphragm (DPH) and rib cage (RC), nor differences to normal breathing are yet understood. This study aims to compare respiratory dynamics in phonation and breathing via dynamic MRI of the lung. Images of the breathing apparatus of 6 professional singers were captured in a 1.5T MRI system in supine position during vital capacity breathing and maximal long sustained phonation at 3 different pitches and loudness conditions. In a dynamic series of cross-sectional images of the lung, distances between characteristic anatomical landmarks were measured. During exhalation in normal breathing the diaphragm and rib cage moved synchronously to reduce lung volume, but during phonation different functional units could be identified, which support phonation by facilitating the control of subglottic pressure.

Comparison of margin of safety following two different techniques of preoxygenation.

Background and Aims:Shortening the duration of efficacious preoxygenation would provide benefit in emergency situations like fetal distress etc. This study aims to compare the margin of safety following preoxygenation using 8 vital capacity breaths (VCB) in 1 min and tidal volume breathing (TVB) for 3 min, by assessing changes in PaO2 and apnea induced desaturation time.Material and Methods:Patients were randomly divided into Group A and B. In Group A, 3 min of TVB using O2 flow of 5 l/min and in Group B, 8 VCB in 60 s using O2 flow of 10 l/min were used. Anesthesia was induced in all patients with propofol followed by succinylcholine 2 mg/kg intravenously. Mask ventilation was not done and following intubation endotracheal tube was kept open to atmosphere. The time taken for the patients to desaturate to 90% was noted and immediately ventilation was resumed. Arterial blood gas samples were taken while patients were breathing room air, immediately after preoxygenation and at 90% desaturation.Results:Baseline PaO2 of both the groups were comparable. After preoxygenation Group B had a significantly high PaO2 value than Group A (439.05 ± 62.20 vs. 345.16 ± 20.80). At 90% desaturation there was no significant difference between groups. Group B showed a significantly high apnea induced desaturation time when compared to Group A (6.87 ± 1.78 vs. 3.47 ± 0.38 min).Conclusions:Preoxygenation by 8 VCB in 1 min provides a greater margin of safety, as it results in a significantly high PaO2 with an almost doubled apnea induced desaturation time, in comparison with TVB for 3 min.

A comparative study of vital capacity breath inhalation with sevoflurane versus intravenous propofol to aid laryngeal mask airway insertion in adults

Background: Laryngeal mask airway has already gained widespread acceptance as an alternative airway device and conduit for endotracheal intubation. Insertion of this Supraglottic Airway Device (SAD) to provide and maintain a seal around the laryngeal inlet for spontaneous ventilation as well as modest level of positive pressure ventilation requires a sufficient depth of anaesthesia and depression of airway reflexes to avoid adverse reactions like gagging, coughing, head and limb movements etc. This study was conducted with the intent to compare Vital Capacity Breath (VCB) inhalation with 8% sevoflurane versus intravenous (IV) propofol for quality and ease of insertion of Laryngeal Mask Airway (LMA) and associated complications Methods: In this prospective, randomized study, 80 adult patients of ASA physical status I and II aged between 20 to 50 years, body weight 0.05).

Techniques of preoxygenation in patients with ineffective face mask seal

Background:Ineffective face mask seal is the most common cause for suboptimal pre-oxygenation. Room air entrainment can be more with vital capacity (VC) breaths when the mask is not a tight fit.Aims:This study was designed to compare 5 min tidal volume (TV) breathing and eight VC breaths in patients with ineffective face mask seal.Methods:Twenty eight ASA I adults with ineffective face mask seal were randomized to breathe 100% oxygen at normal TV for 5 min (Group TV) and eight VC breaths (Group VC) in a cross over manner through circle system at 10 L/min. End tidal oxygen concentration (EtO2) and arterial blood gas analysis was performed to evaluate oxygenation with each technique.Statistical and Analysis:Data were analysed using SPSS statistical software, version 16. Friedman's two-way analysis of variance by ranks was used for non-parametric data.Results:Significant increase in EtO2 (median 90) and PaO2 (228.85) was seen in group TV when compared to group VC (EtO2 median 85, PaO2 147.65), P<0.05. Mean total ventilation volume in 1 min in group VC was 9.4±3.3 L/min and more than fresh gas flow (10 L/min) in seven patients. In group TV, the fresh gas flow (50 L/5 min) was sufficient at normal TV (mean total ventilation in 5 min 36.7±6.3 L/min).Conclusions:TV breathing for 5 min provides better pre-oxygenation in patients with ineffective mask seal with fresh gas flow of 10 L/min delivered through a circle system.

Volitional pursed lips breathing in patients with stable chronic obstructive pulmonary disease improves exercise capacity

Pursed lips breathing (PLB) is used by a proportion of patients with chronic obstructive pulmonary disease (COPD) to alleviate dyspnea. It is also commonly used in pulmonary rehabilitation. Data to support its use in patients who do not spontaneously adopt PLB are limited. We performed this study to assess the acute effects of PLB on exercise capacity in nonspontaneously PLB patients with stable COPD. We performed a randomized crossover study comparing 6-min walk test (6MWT) at baseline without PLB with 6WMT using volitional PLB. Spirometry, maximal inspiratory and expiratory mouth pressures, and diaphragmatic excursion during tidal and vital capacity breathing using B-mode ultrasonography were measured at baseline and after 10 min of PLB. A Visual Analog Scale (VAS) assessed subjective breathlessness at rest, after 6MWT and after 6MWT with PLB. p ≤ 0.01 was considered significant. Mean ± SD age of patients was 53.1 ± 7.4 years. Forced expiratory volume in 1 second was 1.1 ± 0.4 L/min (38.4 ± 13.2% predicted). Compared with spontaneous breathing, all but one patient with PLB showed a significant increment in 6MW distance (+34.9 ± 26.4 m; p = 0.002). There was a significant reduction in respiratory rate post 6MWT with PLB compared with spontaneous breathing (-4.4 ± 2.8 per minute; p = 0.003). There was no difference in VAS scores. There was a significant correlation between improvement in 6MWT distance and increase in diaphragmatic excursion during forced breathing. The improvement was greater in patients who had poorer baseline exercise performance. PLB has an acute benefit on exercise capacity. Sustained PLB or short bursts of PLB may improve exercise capacity in stable COPD.

Sex-related differences in the relationship between acceleromyographic adductor pollicis train-of-four ratio and clinical manifestations of residual neuromuscular block: a study in healthy volunteers during near steady-state infusion of mivacurium

Studies in volunteers suggest that train-of-four (TOF) ratios >0.9 are needed to retain normal function of muscles involved in upper airway patency, swallowing, and vital capacity breathing. We determined if sex-related differences exist in the relationship between adductor pollicis (AP) TOF ratio and measures of neuromuscular function commonly used to assess recovery from neuromuscular block. In 10 males and 10 females, three steady-state levels of neuromuscular block were achieved with mivacurium infusions. TOF ratio was measured with acceleromyography at the AP. Hand grip strength and the ability to clench the teeth, raise the head >5 s, swallow, protrude the tongue, and open the eyes were tested at each stable block level and reconciled to uncorrected and normalized (pre-paralysis values) TOF measures. These relationships were compared between sexes. The ability to clench teeth and head raise >5 s was lost at a significantly greater TOF ratio in males than females. The percentage decrease in handgrip strength with decreasing TOF ratio was proportionally greater in males than females. Forty per cent of the males were unable to clench the teeth at an uncorrected TOF ratio >0.9. When TOF ratios were normalized, clinical functions showed no decrement at TOF ratio >0.9 in any volunteer. Sex-related differences exist in the relationship between AP TOF ratio and clinical measures of muscle function used to assess recovery from neuromuscular block. Normalization of AP TOF ratios is recommended because a non-normalized TOF ratio of 0.9 does not guarantee adequate reversal of neuromuscular block.

Intravenous landiolol, a novel β 1-adrenergic blocker, reduces the minimum alveolar concentration of sevoflurane in women

Study Objective To investigate the effect of intravenous (IV) landiolol, a novel β 1-adrenergic blocker, on the minimum alveolar concentration (MAC) of sevoflurane in adult women. Design Prospective, randomized study. Setting University hospital. Patients 42 ASA physical status 1 and 2 women, aged 24-57 years, who were scheduled to undergo elective abdominal surgery. Interventions Anesthesia was induced in all patients by vital capacity rapid inhalation induction of sevoflurane. In the landiolol group, administration of landiolol began when patients took a vital-capacity breath: 0.125 mg/kg/min for one minute and then 0.04 mg/kg/min. Normal saline was administered in the control group. Measurements MAC was determined by a technique adapted from the conventional up-down method. Main Results The MAC of sevoflurane was 2.2% ± 0.2% in the control group and 1.7% ± 0.2% in the landiolol group, a statistically significant difference ( P = 0.0005). Conclusions IV landiolol reduces the MAC of sevoflurane in women by approximately 20%.

Influence from breathing pattern on alcohol and tracer gas expirograms—Implications for alcolock use

Measurement of breath alcohol concentration is strongly influenced by timing and the breathing pattern. In particular, shallow expiration and hyperventilation leads to underestimation of the breath alcohol concentration. In the present study, expirograms of alcohol, water and carbon dioxide were recorded in 30 healthy individuals at various breathing manoeuvres (tidal volume, slow maximum and vital capacity expiration, breath holding, and hyperventilation). Estimation of the end expiratory alcohol concentration with the use of simultaneously measured carbon dioxide was shown to reverse the tendency of underestimation at shallow expiration and hyperventilation. These findings indicate that breath alcohol estimations can be performed at shorter expiration time and reduced expired volume compared to existing alcolocks. This is believed to improve their usability and to prevent a possible route for manipulation.

Factors influencing oxygen store during denitrogenation in the healthy patient

Study Objective To define the various factors that influence the rate of effective preoxygenation. Design Prospective, randomized study. Setting Procedure room in a teaching hospital. Subjects 14 ASA physical status I volunteers who performed 4 sessions of breathing in random order. Of these volunteers, 7 performed two extra sessions using vital capacity breathing, which were also completed in random order. Interventions Using the circle system, volunteers breathed with a mouthpiece and nose-clip until expired nitrogen reached 5%, using either a fresh gas flow of 5 L/min or 10 L/min or a system flushed with O 2. Measurements End-expired levels of O 2, nitrogen, and CO 2 were recorded. Main Results Minute ventilation, functional residual capacity, and age were significant factors for rate of denitrogenation. However, height and weight were not significant factors in predicting time to denitrogenation. At low flow rates, flushing with O 2 significantly decreased the time of denitrogenation. There appeared to be little clinical benefit of flushing with O 2 when a 10 L/min O 2 flow was used. Conclusions A high gas flow rate appears critical to achieving rapid preoxygenation.

Women with diarrhoea-predominant irritable bowel syndrome show an increased pressure response to 35% carbon dioxide stress challenge

The responses to inhalation of 35% carbon dioxide (CO2) as a stressor were compared in female irritable bowel syndrome (IBS) patients and healthy controls to assess potential differences in cardiovascular, neuroendocrine and behavioural responses to stress. A total of 22 women (12 patients with ROME II defined diarrhoea-predominant IBS and 10 aged-matched controls) were challenged with a single vital capacity breath of 35% CO2 (with 65% oxygen). Beat-to-beat blood pressure and heart rate were recorded prior to, during and after the inhalation. Serum cortisol concentration and behavioural ratings were measured pre- and post-inhalation. A typical pattern of responses to CO2 was observed, characterised by a reduction in heart rate and increases in serum cortisol and anxiogenic symptoms; however, these responses did not differ between groups. Both groups also demonstrated an increase in systolic blood pressure; however, this response was significantly enhanced in IBS patients compared to healthy controls (P < 0.05). These findings demonstrate that females with diarrhoea-predominant IBS have an exaggerated pressor response to 35% CO2 stress challenge, suggesting a more stress-responsive sympathetic nervous system.

Study Of Effects Of Varying Durations Of Pre-Oxygenation

200 ASA grade I and II patients in the age group of 18 to 50 years were studied under four equal groups. Group I patients did not receive any pre-oxygenation; Group-II patients received pre-oxygenation in the form of four vital capacity breaths; Group III and IV patients received pre-oxygenation for 3 and 5 minutes respectively. All the result were compared statistically using Analysis of Variance (ANOVA) method It was observed that the percentage of fall of Sp02 was less in group III and group IV (92.84% and 97.04%) as compared to Group I and Group II (80.66% and 87.94%) suggesting vital role of preoxygenation before induction.

Single Vital-capacity and Successive Tidal-volume Breathing of Sevoflurane in Induction of Anesthesia for Tracheal Intubation in Gynecologic Patients

The optimal end-tidal concentrations of sevoflurane in induction of anesthesia for tracheal intubation have been widely studied and discussed. Single vital-capacity breathing of a high concentration of inspiratory sevoflurane rapidly elevates the end-tidal concentration to cause loss of consciousness, although it does not bear relation to proportional body or brain uptake. This study was designed to investigate the time effect of fast wash-in of alveolar sevoflurane in induction of anesthesia for tracheal intubation with single vital-capacity and ensuing tidal-volume breathing in gynecologic patients. Thirty-six ASA I-II patients undergoing gynecologic surgeries under general anesthesia were included in the study. Prior to anesthesia, they were instructed on the vital capacity technique for induction with prior primed 7.2% inspiratory sevoflurane in 6 L/min oxygen in the breathing circuit. Immediately after loss of consciousness, assisted ventilation with fixed 3.5% sevoflurane in oxygen was applied to patients in groups 1 and 2 for 3 minutes, and for 4.5 minutes in group 3. Patients in group 2 received fentanyl 1.5 mug/kg before induction. In all patients, tracheal intubation was performed following succinylcholine 1.5 mg/kg. Inspiratory and end-tidal concentrations of sevoflurane, blood pressure and heart rate were recorded. All patients achieved vital capacity induction uneventfully, of whom two-thirds needed a second or third breath. The induction time was 60.6 +/- 19.2 seconds and could be reduced to 48.3 +/- 17.9 seconds with fentanyl pretreatment. The end-tidal concentration of sevoflurane was 2.68 +/- 0.20% after 4.5 minutes of ventilation with 3.5% sevoflurane, at which concentration the intubation-induced hemodynamic responses could not be suppressed. This study demonstrated that vital-capacity induction with a high concentration of sevoflurane is a safe and feasible technique for our female patients. The end-tidal 1.5 minimum alveolar concentration sevoflurane following 4.5 minutes of tidal-volume ventilation did not suppress intubation-induced hemodynamic responses. Pretreatment with fentanyl helped to shorten the induction time and provide better hemodynamic control for tracheal intubation.

Pre‐oxygenation in pregnancy: an investigation using physiological modelling

Hypoxaemia during anaesthetic induction in obstetrics is hazardous for mother and baby, but the onset of desaturation can be delayed by pre-oxygenation. This study investigated pre-oxygenation during pregnancy using computer simulation. The Nottingham Physiology Simulator was configured to replicate normal pregnant physiology. Three pregnant and three non-pregnant subjects were created, representing population variation according to published physiological values. They underwent pre-oxygenation by tidal and vital capacity breathing of 100% oxygen. Pre-oxygenation during tidal breathing proceeded more rapidly in pregnancy, the median [range] time to achieve 95% of the maximum change in P(E)O2 being 1 min 37 s [1:23-1:52] in pregnant subjects, compared to 2 min 51 s [2:28-3:15] in non-pregnant subjects. Vital capacity pre-oxygenation required seven breaths [5-10] in pregnant subjects, compared to six breaths [4-9] in non-pregnant subjects, to achieve the same P(E)O2 as after 95% complete tidal pre-oxygenation. We recommend 2 min of tidal breathing for pre-oxygenation in pregnancy.

Comparison of Propofol and Sevoflurane for Laryngeal Mask Airway Insertion in Elderly Patients

Sevoflurane and propofol have been widely used for anesthesia induction. This study compared the efficacies of sevoflurane and propofol inductions for laryngeal mask airway (LMA) insertion in elderly patients. Ninety patients, aged 60 or more, received anesthesia induction with propofol and with sevoflurane 8% using the vital capacity breath (VCB) or tidal volume breath (TVB) techniques. Hemodynamic changes, induction time, complications, and the quality and ease of LMA insertion were observed. LMA was inserted most, less or least rapidly with propofol (89 +/- 28 s), sevoflurane 8% using the VCB (163 +/- 34 s) or TVB (205 +/- 44 s) techniques, respectively. Anesthesia induction with propofol or sevoflurane 8% using the VCB technique produced either more frequent apnea or greater reduction in mean blood pressure than with sevoflurane 8% using the TVB technique. Sevoflurane 8% using the TVB technique provides a smoother induction with a stable hemodynamic profile, less apnea and technical demand, but requiring longer time for LMA insertion in unpremedicated elderly patients.

Pre-oxygenation: a comparison of two techniques using a Bain system

Pre-oxygenation using a standard technique of tidal breathing for 3 min through a Bain system with a fresh gas flow of 8 l.min-1 was compared with up to six vital capacity breaths from the same system. The technique of vital capacity breaths involved initial expiration to residual volume and use of the oxygen flush throughout controlled full inspirations, ensuring that the reservoir bag remained full. No significant problems were encountered using this method. Although three vital capacity breaths produced significantly inferior pre-oxygenation compared to 3 min of normal breathing, four and five vital capacity breaths were equally effective. With six vital capacity breaths, superior pre-oxygenation was produced. The use of four or more vital capacity breaths with this technique is a reliable and rapid alternative to 3 min of tidal breathing.

Hypotension, Heart Rate Variability, and Altered Autonomic Function

Dallas, Texas. latsont@charter.netThe elegant studies by Hanss et al. 1,2demonstrate that alterations in heart rate variability (HRV) may predict hypotension after spinal anesthesia. The authors found a significant association between an increased ratio of low-frequency HRV (LF) to high-frequency HRV (HF) (i.e. , LF/HF) and subsequent hypotension. A less predictive but still significant relation was found between decreased HF and subsequent hypotension.1In their discussion, the authors briefly compare their results with our previous results3investigating altered autonomic function and hypotension after induction of general anesthesia. Both of these studies demonstrated an association between decreased HF and subsequent hypotension. Although the stronger relation that we found with decreased HF and subsequent hypotension may simply reflect obvious differences in the study conditions (e.g. , general anesthesia vs. spinal anesthesia, different patient populations), it might also relate to the different methods used to quantitate HF.Heart rate variability measurements in the study by Hanss et al. 1are presented using normalized units, where the power in a specific frequency band (e.g. , HF) is normalized by the total power in the HRV spectrum (total HRV) for that patient (i.e. , HF in normalized units =[HF in absolute units]/[total HRV in absolute units]). A patient with decreased HF expressed in absolute units might have a normal value of HF when expressed in normalized units if the total HRV in his or her HRV power spectrum is also reduced (which is often the case in patients with autonomic dysfunction from multiple causes). For this reason, we used absolute measurements of HRV in our study. We found both a significant predictive value of decreased HF for postinduction hypotension and a strong correlation between HF and other measures of autonomic dysfunction. Historically, both absolute and normalized measurements of HRV have been used by different investigators.4Normalized units have advantages when HRV is used to examine “sympathovagal balance” (a major focus of the study of Hanss et al. 1), whereas absolute units have advantages when reflex integrity or “gain” (a major focus of our study) is examined.Did the authors of the current study1examine any possible relation between absolute measurements of HF and subsequent hypotension (or is such an analysis possible with their data)? The relation that they observed with postspinal hypotension and normalized measurements of HF might be even stronger using absolute measurements of HF. A stronger relation, if it exists, would argue that preexisting alterations in reflex integrity or gain might also play a role in hypotension after spinal anesthesia (similar to previous findings with general anesthesia3,5). Furthermore, if a significant predictive relation between absolute measurements of HF and postspinal hypotension does exist, fairly simple clinical tests of autonomic function (e.g. , the change in heart rate with six vital capacity breaths, which is highly correlated with absolute measures of HF3) might also have significant predictive value.Dallas, Texas. latsont@charter.net