Biomedical subjects

David G Silverman

Publications and source records attributed to David G Silverman.

12 recordsLinked to original sources

PubMed2006

The use of joint time frequency analysis to quantify the effect of ventilation on the pulse oximeter waveform.

OBJECTIVE: In the process of determining oxygen saturation, the pulse oximeter functions as a photoelectric plethysmograph. By analyzing how the frequency spectrum of the pulse oximeter waveform changes over time, new clinically relevant features can be extracted. METHODS: Thirty patients undergoing general anesthesia for abdominal surgery had their pulse oximeter, airway pressure and CO(2) waveforms collected (50 Hz). The pulse oximeter waveform was analyzed with a short-time Fourier transform using a moving 4096 point Hann window of 82 seconds duration. The frequency signal created by positive pressure ventilation was extracted using a peak detection algorithm in the frequency range of ventilation (0.08-0.4 Hz = 5-24 breaths/minute). The respiratory rate derived in this manner was compared to the respiratory rate as determined by CO(2) detection. RESULTS: In total, 52 hours of telemetry data were analyzed. The respiratory rate measured from the pulse oximeter waveform was found to have a 0.89 linear correlation when compared to CO(2) detection and airway pressure change. the bias was 0.03 breath/min, SD was 0.557 breath/min and the upper and lower limits of agreement were 1.145 and -1.083 breath/min respectively. The presence of motion artifact proved to be the primary cause of failure of this technique. CONCLUSION: Joint time frequency analysis of the pulse oximeter waveform can be used to determine the respiratory rate of ventilated patients and to quantify the impact of ventilation on the waveform. In addition, when applied to the pulse oximeter waveform new clinically relevant features were observed.

Algorithms↗

PubMed2006

Analysis of the ear pulse oximeter waveform.

OBJECTIVE: For years researchers have been attempting to understand the relationship between central hemodynamics and the resulting peripheral waveforms. This study is designed to further understanding of the relationship between ear pulse oximeter waveforms, finger pulse oximeter waveforms and cardiac output (CO). It is hoped that with appropriate analysis of the peripheral waveforms, clues can be gained to help to optimize cardiac performance. METHODS: Part 1: Studying the effect of cold immersion test on plethysmographic waveforms. Part 2: Studying the correlation between ear and finger plethysmographic waveforms and (CO) during CABG surgery. The ear and finger plethysmographic waveforms were analyzed to determine amplitude, width, area, upstroke and downslope. The CO was measured using continuous PA catheter. Using multi-linear regression, ear plethysmographic waveforms, together with heart rate (HR), were used to determine the CO Agreement between the two methods of CO determination was assessed. RESULTS: Part 1: On contralateral hand immersion, all finger plethysmographic waveforms were reduced, there was no significant change seen in ear plethysmographic waveforms, except an increase in ear plethysmographic width. Part 2: Phase 1: Significant correlation detected between the ear plethysmographic width and other ear and finger plethysmographic waveforms. Phase 2: The ear plethysmographic width had a significant correlation with the HR and CO. The correlation of the other ear plethysmographic waveforms with CO and HR are summarized (Table 5). Multi-linear regression analysis was done and the best fit equation was found to be: CO=8.084 - 14.248 x Ear width + 0.03 x HR+ 92.322 x Ear down slope+0.027 x Ear Area Using Bland & Altman, the bias was (0.05 L) but the precision (2.46) is large to be clinically accepted. CONCLUSION: The ear is relatively immune to vasoconstrictive challenges which make ear plethysmographic waveforms a suitable monitor for central hemodynamic changes. The ear plethysmographic width has a good correlation with CO.

Adult↗

PubMed2006

What is the best site for measuring the effect of ventilation on the pulse oximeter waveform?

The cardiac pulse is the predominant feature of the pulse oximeter (plethysmographic) waveform. Less obvious is the effect of ventilation on the waveform. There have been efforts to measure the effect of ventilation on the waveform to determine respiratory rate, tidal volume, and blood volume. We measured the relative strength of the effect of ventilation on the reflective plethysmographic waveform at three different sites: the finger, ear, and forehead. The plethysmographic waveforms from 18 patients undergoing positive pressure ventilation during surgery and 10 patients spontaneously breathing during renal dialysis were collected. The respiratory signal was isolated from the waveform using spectral analysis. It was found that the respiratory signal in the pulse oximeter waveform was more than 10 times stronger in the region of the head when compared with the finger. This was true with both controlled positive pressure ventilation and spontaneous breathing. A significant correlation was demonstrated between the estimated blood loss from surgical procedures and the impact of ventilation on ear plethysmographic data (r(s) = 0.624, P = 0.006).

Adult↗

PubMed2005

Preoperative beta-blocker use: is titration to a heart rate of 60 beats per minute a consistently attainable goal?

STUDY OBJECTIVE: To quantify the prevalence of perioperative beta-blocker use and its impact on preoperative and preinduction heart rate (HR), in light of the recent publication of specific recommendations regarding perioperative beta-blocker use and desired HR. DESIGN: Retrospective observational study in patients who underwent elective and coronary artery bypass graft (CABG) surgery between January 2001 and March 2002. SETTING: Tertiary-care teaching hospital. MEASUREMENTS: Percentage of eligible patients who received beta-blockers preoperatively and the impact of non-protocol-based beta-blocker therapy on preadmission and preinduction HR were recorded. Differences were assessed with unpaired t test and chi(2) analysis; P < .05 was considered significant, with corrections for multiple comparisons. RESULTS: Of the patients who underwent vascular surgery, 9 had documented prior beta-blocker intolerance. Of the remaining 172 patients, 94.8% had indication for perioperative beta-blocker use. However, only 47.7% of the eligible patients received beta-blockers. Of the 155 CABG patients, 74.2% were taking beta-blockers preoperatively. Only 29% of vascular patients and 32% of CABG patients who were receiving beta-blockers had HR less than 60 beats per minute (bpm) at preadmission. The mean preadmission HR in vascular surgery patients was 65.2 +/- 11 and 73.2 +/- 13.8 bpm in beta-blocker and non-beta-blocker patients, respectively (P = .0001). In CABG surgery patients, preadmission HR values were 64.2 +/- 13 and 76.1 +/- 12 bpm in beta-blocker and non-beta-blocker patients, respectively (P = .001). The preinduction HR subsequently increased in the beta-blocker as well as in the non-beta-blocker groups. CONCLUSION: Only half of the patients who qualify to receive preoperative beta-blockers by current recommendations actually receive them before noncardiac surgery, and the majority of these patients have preadmission and preinduction HR less than 60 bpm. Targeting beta-blocker therapy treatment to an HR less than 60 bpm may not be readily achievable in many patients.

Adrenergic beta-Antagonists↗

PubMed2005

The effect of venous pulsation on the forehead pulse oximeter wave form as a possible source of error in Spo2 calculation.

Reflective forehead pulse oximeter sensors have recently been introduced into clinical practice. They reportedly have the advantage of faster response times and immunity to the effects of vasoconstriction. Of concern are reports of signal instability and erroneously low Spo(2) values with some of these new sensors. During a study of the plethysmographic wave forms from various sites (finger, ear, and forehead) it was noted that in some cases the forehead wave form became unexpectedly complex in configuration. The plethysmographic signals from 25 general anesthetic cases were obtained, which revealed the complex forehead wave form during 5 cases. We hypothesized that the complex wave form was attributable to an underlying venous signal. It was determined that the use of a pressure dressing over the sensor resulted in a return of a normal plethysmographic wave form. Further examination of the complex forehead wave form reveal a morphology consistent with a central venous trace with atrial, cuspidal, and venous waves. It is speculated that the presence of the venous signal is the source of the problems reported with the forehead sensors. It is believed that the venous wave form is a result of the method of attachment rather than the use of reflective plethysmographic sensors.

Female↗

PubMed2004

Assessment and management of patients with ischemic heart disease.

OBJECTIVE: Review the perioperative management of patients who are scheduled for noncardiac surgery. DATA SOURCE: Review of literature (PubMed, MEDLINE). CONCLUSIONS: Patients with ischemic heart disease who undergo noncardiac surgery are at significant risk of perioperative cardiac morbidity and mortality. Recent joint guidelines from the American College of Cardiology and American Heart Association have significantly streamlined the preoperative evaluation processes. Augmented hemodynamic control with intensive perioperative pharmacologic therapy with beta-blockers and possibly alpha-2 agonist has been shown to improve perioperative cardiovascular outcomes. However, translating this information to clinical practice continues to be a challenge and requires a multi- disciplinary approach. A particular intraoperative anesthetic technique is unlikely to influence perioperative cardiac morbidity and mortality. Postoperative management with goals of decreasing hemodynamic stress is important in patients with ischemic heart disease. Diagnosis and management of perioperative myocardial infarction continues to be a challenge. However, use of cardiac specific biomarkers should improve the diagnostic process.

Adrenergic beta-Antagonists↗

PubMed2004

Optimizing postoperative outcomes with efficient preoperative assessment and management.

OBJECTIVE: To review the essential features of preoperative assessment, management, and planning, with special emphasis on high-risk patients who are likely to have manifestations related to their co-existing disease and disease treatment(s) in the postoperative setting. DATA SOURCE: Review of recent studies and reviews as reprinted in Index Medicus. CONCLUSIONS: The major shift in preoperative assessment and management from within the hospital to outside the hospital has prompted new efforts to coordinate preoperative care. Much of this can be accomplished with the introduction of a preadmission testing center. Under the direction of a physician (typically an anesthesiologist), the Pre-Admission Testing Center staff performs necessary assessments and coordinates necessary information about the presurgical patient. This assessment should include features essential to the general history and physical examination, as well as the specific issues related to anesthesia and surgery. The preoperative visit is also an opportunity to perform directed laboratory testing (as opposed to across the board batteries of tests) and to carefully plan out the continuance, discontinuance, or initiation of medications in the perioperative period. It also may be beneficial to stabilize disorders such as hypertension and, when indicated, initiate preoperative optimization of patients with advanced disease. The ultimate goal is to provide safe and "efficient" care, without exhausting highly valued intensive care resources.

Anesthesiology↗

PubMed2004

Recovery of neuromuscular function after a combination of mivacurium and rocuronium.

PURPOSE: The present study was undertaken to evaluate onset, and early and late recovery of neuromuscular block after a combination of mivacurium (M) and rocuronium (R). METHODS: In this controlled, randomized study, 45 consenting ASA I-II patients were assigned to one of three treatment groups: 2.ED95 R alone (2R); 2.ED95 R plus 1.ED95 M (2R1M). or 2.ED95 R plus 2.ED95 M (2R2M). Neuromuscular monitoring of the ulnar nerve consisted of surface electrode stimulation and force transduction of the adductor pollicis muscle. Stable baseline stimulation (1 Hz, square-wave, supramaximal current) was established prior to relaxant administration and continued until 95 percent twitch height depression (onset). Thereafter, train-of-four stimulation every 10 seconds was used to record recovery data until 95 percent recovery (T(95%)). Data were analyzed using grouped t-tests, ANOVA, and Newman-Keuls multiple comparison tests. Significance was defined at the p < 0.05 level. RESULTS: The addition of mivacurium to rocuronium did not accelerate onset of block. The combination prolonged the clinical duration (time to 5 percent recovery, T(5%)), but did not affect subsequent recovery parameters: T(5%) in the 2R1M and 2R2M groups were 100 percent and 118 percent longer than in the 2R group, respectively (p < 0.05) the T(5-25%) (early recovery) and T(25-75%) (linear recovery) indexes were similar in all three groups. CONCLUSIONS: The present study did not note an acceleration of block onset when mivacurium was added to rocuronium. The findings suggest that the addition of mivacurium (1-2.ED95) to rocuronium (2.ED95) prolongs the clinical duration of the longer-acting agent, rocuronium, but has no effect on the early or linear recovery indexes of rocuronium. Thus, although clinical duration is prolonged, recovery from the combination regimens proceeds as if no mivacurium had been added to rocuronium.

Adolescent↗

PubMed2003

Intradermal sufentanil does not improve lidocaine-induced local anesthesia.

PURPOSE: Peripheral opioid receptors may result in antinociceptive effects when occupied by opioids. This study examined intradermally injected sufentanil (S), a highly lipid soluble opioid, administered with and without lidocaine (L), in a thermal pain model. METHODS: Nine volunteers were instructed on the method of magnitude estimation of pain before undergoing baseline testing with seven seconds thermal stimuli between 44 and 52 degrees C, delivered by a contact thermal stimulator at five cutaneous forearm sites. Then, four sites randomly received injections of equal volumes (0.1 mL) of either normal saline (NS), lidocaine 0.5% (L), sufentanil 0.75 microg (S), lidocaine 0.5% plus sufentanil 0.75 microg (L+S), and one site was not injected and served as reference (REF). Testing was repeated at six, 30, 60, 90, 120, and 150 min following injection. The pain elicited by each stimulus was normalized to the subject's response to the 50 degrees C stimulus at the REF site. RESULTS: Baseline testing showed small (P = ns) differences in pain scores. At six minutes, the lidocaine sites (L, L+S) had pain scores that were mean 83% (range 78-88%) lower than the other sites (P < 0.05), but there was no difference between the L and L+S sites or between the S and NS or REF sites. At 30 and 60 min these pain scores were mean 38% (29-44%) and 20% (8-30%) less than at the REF, NS, and S sites (P = ns). At 90 min and later times, the pain scores had returned to baseline. CONCLUSIONS: These results suggest that intradermal sufentanil alone has no analgesic effect. Further, in combination with lidocaine, sufentanil does neither potentiate nor prolong the analgesic effect of lidocaine.

Adult↗

PubMed2003

Rofecoxib does not compromise platelet aggregation during anesthesia and surgery.

PURPOSE: This study was undertaken because, although there is evidence that cyclooxygenase type 2 (COX)-2 inhibitors do not compromise platelets in healthy volunteers, many clinicians remain hesitant to administer them perioperatively without definitive evidence of intact platelet function during anesthesia and surgery. METHODS: In 20 patients scheduled for lower abdominal and pelvic surgery, 5 mL of blood were obtained for baseline platelet aggregometry. One hour prior to surgery, patients received an oral solution of either rofecoxib (ROF) 50 mg or placebo (PLAC) by randomized, double-blinded assignment. Approximately one hour after onset of anesthesia, an intraoperative blood sample was obtained. Baseline and postdrug samples were centrifuged to generate platelet-rich plasma, which was challenged with adenosine diphosphate (ADP) and arachidonic acid (AA). Aggregometry was performed with and without incubation with aspirin. The data in each subject were normalized to baseline aggregation in response to AA alone and ADP alone. Intergroup differences were assessed using paired t test; P < 0.05 was considered significant. RESULTS: Consistent with known effects of anesthesia on platelet function, both groups had approximately 25% intraoperative declines in aggregation in response to ADP (P = NS for PLAC vs ROF) and even greater declines in response to AA (P = NS for PLAC vs ROF). Aspirin eliminated aggregation in response to AA in both groups (P = NS), and it caused similar declines in PLAC and ROF groups during exposure to ADP (P = NS). CONCLUSION: This study provides strong evidence that ROF does not compromise platelet aggregation during anesthesia and surgery; nor does it interfere with the platelet inhibitory effect of aspirin.

Abdomen↗

PubMed2002

Distinction between atropine-sensitive control of microvascular and cardiac oscillatory activity.

This study tested whether "high frequency" oscillations (HF; >0.12 cycles/s) in microvascular flow during a vasoconstrictive challenge constitute a homeostatic cholinergic response at the level of the microvasculature or simply represent oscillations that originate at the heart and are transmitted to passive microvascular beds. Heart rate, blood pressure, respiratory rate, and laser Doppler flowmetry of the forehead and finger were monitored in healthy volunteers at baseline, during systemic infusion of phenylephrine (0.4-0.6 microg/kg/min), and during subsequent addition of intravenous atropine (< or = 2.0 mg/70 kg). Spectral-domain analysis documented that atropine-sensitive oscillatory power of the R-wave to R-wave intervals of the electrocardiogram was predominant at the respiratory frequency (0.20 Hz) at baseline and during phenylephrine infusion. In contrast, arteriolar-capillary networks of the forehead developed a prominent atropine-sensitive oscillatory peak at 0.14 +/- 0.02 Hz during phenylephrine infusion (P < 0.05 for differences in oscillatory magnitude and frequency between forehead flow and R-R intervals). The cross-power spectral density confirmed the lack of common power between forehead flow and R-R oscillations. Post hoc assessments showed that---similar to heart rate---systemic pressure and systemic flow also had persistent power at 0.20 Hz and did not develop a peak at the forehead oscillatory frequency; phenylephrine likewise did not induce atropine-sensitive oscillations in the finger, a finding attributable to adrenergic predominance in this region. We conclude that atropine-sensitive oscillatory activity in the forehead microvasculature in response to a vasoconstrictive challenge constitutes a local response that is not due to, nor associated with, mechanical transmission from the heart and proximal vasculature.

Atropine↗

PubMed2002

Synchronous rhythmical vasomotion in the human cutaneous microvasculature during nonpulsatile cardiopulmonary bypass.

BACKGROUND: The origin, control mechanisms, and functional significance of oscillations in microvascular flow are incompletely understood. Although the traditional belief has been that only low-frequency oscillations (0.04-0.10 Hz) can originate at the microvascular level, recent evidence in healthy volunteers has suggested that high-frequency oscillations (> 0.10 Hz) also may have a microvascular origin (as opposed to being mechanically transmitted respiratory-induced variations in stroke volume). The current study determined if such oscillations would emerge in the absence of cardiac and respiratory activity during nonpulsatile cardiopulmonary bypass (NP-CPB). METHODS: Forehead and finger laser Doppler flow, arterial pressure, and core temperature were simultaneously recorded in eight patients during NP-CPB. Analyses included time- domain indices, frequency-domain indices (auto power spectral density), and a measure of regularity (approximate entropy) for standardized time segments. RESULTS: Nonpulsatile cardiopulmonary bypass was associated with the emergence of rhythmical oscillations in laser Doppler flow, with characteristic frequencies for the forehead (0.13 +/- 0.03 Hz) and finger (0.07 +/- 0.02 Hz). Forehead vasomotion became progressively synchronized, with a gain in high-frequency spectral power from 17.5 (minute 1) to 89.1 (minute 40) normalized units, and a decrease in approximate entropy from 1.2 (before NP-CPB) to less than 0.5 (minute 40). CONCLUSIONS: The emergence of forehead microvascular oscillations at greater than 0.10 Hz (characteristic of parasympathetic frequency response), in the absence of cardiac and respiratory variability, demonstrates their peripheral origin and provides insights into parasympathetic vasoregulatory mechanisms. The progressive synchronization of forehead vasomotion during NP-CPB, suggestive of increased coupling among microvascular biologic oscillators, may represent a microcirculatory homeostatic response to systemic depulsation, with potential implications for end-organ perfusion.

Aged↗