Interactions between heart rate variability and pulmonary gas exchange efficiency in humans.

The respiratory component of heart rate variability (respiratory sinus arrhythmia, RSA) has been associated with improved pulmonary gas exchange efficiency in humans via the apparent clustering and scattering of heart beats in time with the inspiratory and expiratory phases of alveolar ventilation, respectively. However, since human RSA causes only marginal redistribution of heart beats to inspiration, we tested the hypothesis that any association between RSA amplitude and pulmonary gas exchange efficiency may be indirect. In 11 patients with fixed-rate cardiac pacemakers and 10 healthy control subjects, we recorded R-R intervals, respiratory flow, end-tidal gas tension and the ventilatory equivalents for carbon dioxide and oxygen during 'fast' (0.25 Hz) and 'slow' paced breathing (0.10 Hz). Mean heart rate, mean arterial blood pressure, mean arterial pressure fluctuations, tidal volume, end-tidal CO(2), and were similar between pacemaker and control groups in both the fast and slow breathing conditions. Although pacemaker patients had no RSA and slow breathing was associated with a 2.5-fold RSA amplitude increase in control subjects (39 +/- 21 versus 97 +/- 45 ms, P < 0.001), comparable (main effect for breathing frequency, F(1,19) = 76.54, P < 0.001) and reductions (main effect for breathing frequency, F(1,19) = 23.90, P < 0.001) were observed for both cohorts during slow breathing. In addition, the degree of (r = 0.36, P = 0.32) and reductions (r = 0.29, P = 0.43) from fast to slow breathing were not correlated to the degree of associated RSA amplitude enhancements in control subjects. These findings suggest that the association between RSA amplitude and pulmonary gas exchange efficiency during variable-frequency paced breathing observed in prior human work is not contingent on RSA being present. Therefore, whether RSA serves an intrinsic physiological function in optimizing pulmonary gas exchange efficiency in humans requires further experimental validation.

Paradoxical respiratory sinus arrhythmia in the anesthetized rat.

This study examines respiratory sinus arrhythmia (RSA) in the isoflurane-anesthetized rat. In fifteen female Sprague-Dawley rats, we recorded continuous ECG and respiratory airflow before and after bilateral vagotomy. RSA was assessed using power spectral analysis and by plotting the normalised changes in heart period as a function of the time during the respiratory cycle. Contrary to descriptions of RSA in conscious rats, we observed in all rats in the current study a 'reversed' pattern of RSA in which heart rate decelerated during inspiration. Elimination of vagal efferent fibres to the heart by vagotomy did not abolish the presence of reversed RSA suggesting that the pattern of heart period variation is not neural, and may be largely mechanical. Vagotomy altered breathing by increasing respiratory period, tidal volume, and the time to peak inspiratory flow. These changes did not alter the magnitude of RSA but reduced the latency period between inspiratory onset and the onset of respiratory related prolongation of heart period. Periods of positive pressure ventilation were associated with reversal of the inspiratory cardiac-deceleration pattern of RSA to resemble the more widely described pattern of inspiratory cardiac-acceleration. We conclude that RSA is not a suitable measure of vagal tone during anesthesia in the rat and reiterate the caution that needs to be taken when working with anesthetized experimental models of cardiac control.

Agreement of clinical measurements of liver size with ultrasound when performed by medical students.

AIM: The accuracy of physical examination techniques in detecting liver disease is unclear. We sought to determine the perceived location of the lower liver border via scratch, percussion, palpation and ballottement with novice medical student examiners, compared with ultrasound localisation. METHOD: Five novice medical students learnt four liver examination techniques and measured the lower liver border in 19 healthy volunteers. The difference between the examination technique and ultrasound (bias) and limits of agreement of each method were estimated by mixed linear models and shown using Bland-Altman- like plots. RESULTS: All techniques had similar bias for the lower liver border, between 1.6 and 1.9 cm superior to the ultrasound measurement. Percussion had the smallest variability with increasing liver size. Limits of agreement were wide for all techniques, smallest for palpation (6.04 cm) and largest for scratch (7.2 cm) compared to the mean liver distance of 8 cm. Conclusion There was no difference in bias between the scratch, percussion, palpation and ballottement techniques regarding the lower liver border. All techniques had very wide limits of agreement, although palpation had the smallest. Liver size examination by novice medical students in healthy subjects is unreliable. Further research is needed using examiners with a different level of expertise and participants of varying body habitus and confirmed liver disease.

Cardiac baroreflex gain is frequency dependent: insights from repeated sit-to-stand maneuvers and the modified Oxford method.

Cardiac baroreflex gain is usually quantified as the reflex alteration in heart rate during changes in blood pressure without considering the effect of the rate of change in blood pressure on the estimated gain. This study sought to (i) characterize baroreflex gain as a function of blood pressure oscillation frequencies using a repeat sit-to-stand method and (ii) compare baroreflex gain values obtained using the sit-to-stand method against the modified Oxford method. Fifteen healthy individuals underwent the repeated sit-to-stand method in which blood pressure oscillations were driven at 0.03, 0.05, 0.07, and 0.1 Hz. Sixteen healthy participants underwent the sit-to-stand and modified Oxford methods to examine their agreement. Sit-to-stand baroreflex gain was highest at 0.05 Hz (8.8 ± 3.2 ms·mm Hg(-1)) and lowest at 0.1 Hz (5.8 ± 3.0 ms·mm Hg(-1)). Baroreflex gains at 0.03 Hz (7.7 ± 3.0 ms·mm Hg(-1)) and 0.07 Hz (7.5 ± 3.3 ms·mm Hg(-1)) were not different from the baroreflex gain at 0.05 Hz. There was moderate correlation between phenylephrine gain and sit-to-stand gain (r values ranged from 0.52 to 0.75; all frequencies, p < 0.05), but no correlation between sodium nitroprusside gain and sit-to-stand gain (r values ranged from -0.07 to 0.22; all p < 0.05). Bland-Altman analysis of phenylephrine gain and sit-to-stand gain showed poor agreement and a positive proportional bias. These results show that baroreflex gains derived from these 2 methods cannot be used interchangeably. Furthermore, cardiac baroreflex gain is frequency dependent between 0.03 Hz and 0.1 Hz, which challenges the conventional practice of summarizing baroreflex gain as a single number.

Junior doctor skill in the art of physical examination: a retrospective study of the medical admission note over four decades.

OBJECTIVES: To investigate the hypothesis that junior doctors' examination skills are deteriorating by assessing the medical admission note examination record. DESIGN: Retrospective study of the admission record. SETTING: Tertiary care hospital. METHODS: The admission records of 266 patients admitted to Wellington hospital between 1975 and 2011 were analysed, according to the total number of physical examination observations (PEOtot), examination of the relevant system pertaining to the presenting complaint (RelSystem) and the number of body systems examined (Nsystems). Subgroup analysis proceeded according to admission year, level of experience of the admitting doctor (registrar, house surgeon (HS) and trainee intern (TI)) and medical versus surgical admission notes. Further analysis investigated the trend over time in documentation with respect to cardiac murmurs, palpable liver, palpable spleen, carotid bruit, heart rate, funduscopy and apex beat location and character. RESULTS: PEOtot declined by 34% from 1975 to 2011. Surgical admission notes had 21% fewer observations than medical notes. RelSystem occurred in 94% of admissions, with no decline over time. Medical notes documented this more frequently than surgical notes (98% and 86%, respectively). There were no differences between registrars and HS, except for the 2010s subgroup (97% and 65%, respectively). Nsystems declined over the study period. Medical admission notes documented more body systems than surgical notes. There were no differences between registrars, HSs and TIs. Fewer examinations were performed for palpable liver, palpable spleen, cardiac murmur and apex beat location and character over the study period. There was no temporal change in the positive findings of these observations or heart rate rounding. CONCLUSIONS: There has been a decline in the admission record at Wellington hospital between 1975 and 2011, implying a deterioration in local doctors' physical examination skills. Measures to counter this trend are discussed.

Cardioventilatory coupling in preterm and term infants: effect of position and sleep state.

This study documented the effect of position on cardioventilatory coupling (CVC), the triggering of inspiratory onset by a preceding heartbeat, in infants. Cardiorespiratory signals and corresponding oxygen saturation (SpO(2)) were downloaded from Quiet Sleep (QS) and Active Sleep (AS) in prone and supine from preterm (PT) and term (T) infants. Inspiratory onsets (I) and timing of the corresponding ECG R wave were determined and R-R and R-I intervals calculated. The RI(-1) interval (time between inspiration and the preceding R wave) dispersion was measured using proportional Shannon Entropy of the RI(-1) interval (SH(α)), to provide a quantitative measure of CVC. CVC was more frequently seen in QS in PT (p=0.002) and T (p=0.02) infants but not influenced by position (p=0.71, p=0.46). CVC correlated with SpO(2) in PT (r=-0.230, p=0.03) but not T infants (r=0.085, p=0.34). These data imply an augmentation of cardiac influence on ventilatory rhythm in infants in QS. In preterm infants CVC may have a role in supporting oxygenation.

Peri-operative management of anti-platelet agents.

BACKGROUND: Increasing numbers of patients treated with anti-platelet agents are presenting for non-cardiac surgery. We examined the peri-operative management of anti-platelet therapy in patients undergoing elective non-cardiac surgery and the process by which patients received instructions. METHODS: We interviewed and collected outcome data on 213 consecutive patients aged > or = 45 years presenting for elective non-cardiac surgery at our institution over a 6-week period regarding the peri-operative management of anti-platelet and warfarin therapy. RESULTS: Anti-platelet therapy was prescribed in 22.5% and warfarin in 5.2% of the study subjects. Aspirin was stopped peri-operatively in 55.3%, while clopidogrel was stopped in the sole patient treated with this. The frequency of anti-platelet agent discontinuation was similar for major and minor surgery. Warfarin was discontinued prior to surgery in all cases. Only 54.2% of those treated with anti-platelet therapy recalled being given instruction regarding pre-operative management of their anti-platelet therapy compared with 90.9% of patients treated with warfarin (P= 0.04). In the absence of instructions, a number of patients made their own decision to stop their aspirin pre-operatively. Post-operatively, only 37% recalled receiving instructions regarding restarting anti-platelet therapy. As a result, three patients failed to do so. In contrast, all those treated with warfarin received clear post-operative instructions. CONCLUSION: Peri-operative anti-platelet management and communication with patients appears to be sub-optimal. There is a need for standardized processes whereby informed decisions regarding peri-operative anti-platelet therapy are made and communicated clearly to the patients.