Effects of changes in colored light on brain and calf muscle blood concentration and oxygenation

Color light therapy is a therapeutic method in complementary medicine. In color therapy, light of two contrasting colors is often applied in a sequential order. The aim of this study was to investigate possible physiological effects, i.e., changes in the blood volume and oxygenation in the brain and calf muscle of healthy subjects who were exposed to red and blue light in sequential order. The hypothesis was that if a subject is first exposed to blue and then red light, the effect of the red light will be enhanced due to the contrastingly different characteristics of the two colors. The same was expected for blue light, if first exposing a subject to red and then to blue light. Twelve healthy volunteers (six male, six female) were measured twice on two different days by near-infrared spectroscopy during exposure to colored light. Two sequences of colored light were applied in a controlled, randomized, crossover design: first blue, then red, and vice versa. For the brain and muscle, the results showed no significant differences in blood volume and oxygenation between the two sequences, and a high interindividual physiological variability. Thus, the hypothesis had to be rejected. Comparing these data to results from a previous study, where subjects were exposed to blue and red light without sequential color changes, shows that the results of the current study appear to be similar to those of red light exposure. This may indicate that the exposure to red light was preponderant and thus effects of blue light were outweighed.

Cerebral oxygenation in patients after severe head injury: monitoring and effects of arterial hyperoxia on cerebral blood flow, metabolism and intracranial pressure

Early impaired cerebral blood flow (CBF) after severe head injury (SHI) leads to poor brain tissue oxygen delivery and lactate accumulation. The purpose of this investigation was to elucidate the relationship between CBF, local dialysate lactate (lact(md)) and dialysate glucose (gluc(md)), and brain tissue oxygen levels (PtiO2) under arterial normoxia. The effect of increased brain tissue oxygenation due to high fractions of inspired oxygen (FiO2) on lact(md) and CBF was explored. A total of 47 patients with SHI were enrolled in this studies (Glasgow Coma Score [GCS] < 8). CBF was first assessed in 40 patients at one time point in the first 96 hours (27 +/- 28 hours) after SHI using stable xenon computed tomography (Xe-CT) (30% inspired xenon [FiXe] and 35% FiO2). In a second study, sequential double CBF measurements were performed in 7 patients with 35% FiO2 and 60% FiO2, respectively, with an interval of 30 minutes. In a subsequent study, 14 patients underwent normobaric hyperoxia by increasing FiO2 from 35 +/- 5% to 60% and then 100% over a period of 6 hours. This was done to test the effect of normobaric hyperoxia on lact(md) and brain gluc(md), as measured by local microdialysis. Changes in PtiO2 in response to changes in FiO2 were analyzed by calculating the oxygen reactivity. Oxygen reactivity was then related to the 3-month outcome data. The levels of lact(md) and gluc(md) under hyperoxia were compared with the baseline levels, measured at 35% FiO2. Under normoxic conditions, there was a significant correlation between CBF and PtiO2 (R = 0.7; P < .001). In the sequential double CBF study, however, FiO2 was inversely correlated with CBF (P < .05). In the 14 patients undergoing the 6-hour 100% FiO2 challenge, the mean PtiO2 levels increased to 353 (87% compared with baseline), although the mean lact(md) levels decreased by 38 +/- 16% (P < .05). The PtiO2 response to 100% FiO2 (oxygen reactivity) was inversely correlated with outcome (P < .01). Monitoring PtiO2 after SHI provides valuable information about cerebral oxygenation and substrate delivery. Increasing arterial oxygen tension (PaO2) effectively increased PtiO2, and brain lact(md) was reduced by the same maneuver.

Effects of inner and heard speech in arts speech therapy on cerebral oxygenation and hemodynamics

Background: The aim of the present study was to contributing to researching physiological effects of arts speech therapy by (i) investigating effects of inner and heard speech on cerebral hemodynamics and oxygenation, and (ii) analyzing if these changes were affected by alterations of the arterial carbon dioxide pressure (PaCO2). Methods: In 29 healthy adult volunteers we measured changes in cerebral absolute oxyhemoglobin ([O2Hb]), deoxyhemoglobin ([HHb]), total hemoglobin ([tHb]) concentrations and tissue oxygen saturation (StO2) (over the left and right anterior prefrontal cortex (PFC)) using functional near-infrared spectroscopy (fNIRS) as well as changes in end-tidal CO2 (PETCO2) using capnography. Each subject performed six different tasks: three types of task modalities, i.e. inner speech, heard speech from a person and heard speech from a record, and, two recitation texts, i.e. hexameter and alliteration on different days according to a randomized crossover design. Statistical analysis was applied to the differences between the baseline, two task and four recovery periods. The two brain hemispheres, i.e. left and right PFC, and six tasks were tested separately. Results: During the tasks we found in general a decrease in PETCO2 (significantly only for inner speech), StO2, [O2Hb], [tHb] as well as in an increase in [HHb]. There was a significant difference between hexameter and alliteration. Particularly, the changes in [tHb] at the left PFC during tasks and after them were statistically different. Furthermore we found significant relations between changes in [O2Hb], [HHb], [tHb] or StO2 and the participants’ age, the baseline PETCO2, or certain speech tasks. Conclusions: Changes in breathing (hyperventilation) during the tasks led to lower PaCO2 (hypocapnia) for inner speech. During heard speech no significant changes in PaCO2 occurred, but the decreases in StO2, [O2Hb], [tHb] suggest that changes in PaCO2 were also relevant here. Different verse types (hexameter, alliteration) led to different changes in [tHb]. Consequently, StO2, [O2Hb], [HHb] and [tHb] are affected by interplay of both PaCO2 reactivity and task dependent functional brain activity.

Effects of lung recruitment maneuvers on splanchnic organ perfusion during endotoxin-induced pulmonary arterial hypertension

Lung recruitment maneuvers (RMs), used to reopen atelectatic lung units and to improve oxygenation during mechanical ventilation, may result in hemodynamic impairment. We hypothesize that pulmonary arterial hypertension aggravates the consequences of RMs in the splanchnic circulation. Twelve anesthetized pigs underwent laparotomy and prolonged postoperative ventilation. Systemic, regional, and organ blood flows were monitored. After 6 h (= baseline), a recruitment maneuver was performed with sustained inflation of the lungs. Thereafter, the pigs were randomly assigned to group C (control, n = 6) or group E with endotoxin-induced pulmonary arterial hypertension (n = 6). Endotoxemia resulted in a normotensive and hyperdynamic state and a deterioration of the oxygenation index by 33%. The RM was then repeated in both groups. Pulmonary artery pressure increased during lipopolysaccharide infusion from 17 ± 2 mmHg (mean ± SD) to 31 ± 10 mmHg and remained unchanged in controls (P < 0.05). During endotoxemia, RM decreased aortic pulse pressure from 37 ± 14 mmHg to 27 ± 13 mmHg (mean ± SD, P = 0.024). The blood flows of the renal artery, hepatic artery, celiac trunk, superior mesenteric artery, and portal vein decreased to 71% ± 21%, 69% ± 20%, 76% ± 16%, 79% ± 18%, and 81% ± 12%, respectively, of baseline flows before RM (P < 0.05 all). Organ perfusion of kidney cortex, kidney medulla, liver, and jejunal mucosa in group E decreased to 65% ± 19%, 77% ± 13%, 66% ± 26%, and 71% ± 12%, respectively, of baseline flows (P < 0.05 all). The corresponding recovery to at least 90% of baseline regional blood flow and organ perfusion lasted 1 to 5 min. Importantly, the decreases in regional blood flows and organ perfusion and the time to recovery of these flows did not differ from the controls. In conclusion, lipopolysaccharide-induced pulmonary arterial hypertension does not aggravate the RM-induced significant but short-lasting decreases in systemic, regional, and organ blood flows.

The effects of mechanical ventilation on hepato-splanchnic perfusion

PURPOSE OF REVIEW: Mechanical ventilation is a cornerstone of ICU treatment. Because of its interaction with blood flow and intra-abdominal pressure, mechanical ventilation has the potential to alter hepato-splanchnic perfusion, abdominal organ function and thereby outcome of the most critically ill patients. RECENT FINDINGS: Mechanical ventilation can alter hepato-splanchnic perfusion, but the effects are minimal (with moderate inspiratory pressures, tidal volumes, and positive end-expiratory pressure levels) or variable (with high ones). Routine nursing procedures may cause repeated episodes of inadequate hepato-splanchnic perfusion in critically ill patients, but an association between perfusion and multiple organ dysfunction cannot yet be determined. Clinical research continues to be challenging as a result of difficulties in measuring hepato-splanchnic blood flow at the bedside. SUMMARY: Mechanical ventilation and attempts to improve oxygenation such as intratracheal suctioning and recruitment maneuvers, may have harmful consequences in patients with already limited cardiovascular reserves or deteriorated intestinal perfusion. Due to difficulties in assessing hepato-splanchnic perfusion, such effects are often not detected.

Effects of an alveolar recruitment maneuver on cardiovascular and respiratory parameters during total intravenous anesthesia in ponies

OBJECTIVE: To evaluate pulmonary and cardiovascular effects of a recruitment maneuver (RM) combined with positive end-expiratory pressure (PEEP) during total intravenous anesthesia in ponies. ANIMALS: 6 healthy adult Shetland ponies. PROCEDURE: After premedication with detomidine (10 microg/kg, IV), anesthesia was induced with climazolam (0.06 mg/kg, IV) and ketamine (2.2 mg/kg, IV) and maintained with a constant rate infusion of detomidine (0.024 mg/kg/h), climazolam (0.036 mg/kg/h), and ketamine (2.4 mg/kg/h). The RM was preceded by an incremental PEEP titration and followed by a decremental PEEP titration, both at a constant airway pressure difference (deltaP) of 20 cm H2O. The RM consisted of a stepwise increase in deltaP by 25, 30, and 35 cm H2O obtained by increasing peak inspiratory pressure (PIP) to 45, 50, and 55 cm H2O, while maintaining PEEP at 20 cm H2O. Hemodynamic and pulmonary variables were analyzed at every step of the PEEP titration-RM. RESULTS: During the PEEP titration-RM, there was a significant increase in PaO 2 (+12%), dynamic compliance (+ 62%), and heart rate (+17%) and a decrease in shunt (-19%) and mean arterial blood pressure (-21%) was recorded. Cardiac output remained stable. CONCLUSIONS AND CLINICAL RELEVANCE: Although baseline oxygenation was high, Pa(O2) and dynamic compliance further increased during the RM. Despite the use of high PIP and PEEP and a high tidal volume, limited cardiovascular compromise was detected. A PEEP titration-RM may be used to improve oxygenation in anesthetized ponies. During stable hemodynamic conditions, PEEP titration-RM can be performed with acceptable adverse cardiovascular effects.

Hemodynamic effects of thoracic epidural analgesia in ovine hyperdynamic endotoxemia

BACKGROUND AND OBJECTIVES: Thoracic epidural analgesia (TEA) is increasingly used for perioperative analgesia. If patients with TEA develop sepsis or systemic inflammatory response subsequent to extended surgery the question arises if it would be safe to continue TEA with its beneficial effects of improving gastrointestinal perfusion and augmenting tissue oxygenation. A major concern in this regard is hemodynamic instability that might ensue from TEA-induced vasodilation. The objective of the present study was to assess the effects of TEA on systemic and pulmonary hemodynamics in a sepsis model of hyperdynamic endotoxemia. METHODS: After a baseline measurement in healthy sheep (n = 14), Salmonella thyphosa endotoxin was continuously infused at a rate of 10 ngxkg(-1)xmin(-1) over 16 hours. The surviving animals (n = 12) were then randomly assigned to 1 of 2 study groups. In the treatment group (n = 6), continuous TEA was initiated with 0.1 mLxkg(-1) bupivacaine 0.125% and maintained with 0.1 mLxkg(-1)xh(-1). In the control group (n = 6) the same amount of isotonic sodium saline solution was injected at the same rate through the epidural catheter. RESULTS: In both experimental groups cardiac index increased and systemic vascular resistance decreased concurrently (each P < .05). Functional epidural blockade in the TEA group was confirmed by sustained suppression of the cutaneous (or panniculus) reflex. During the observational period of 6 hours neither systemic nor pulmonary circulatory variables were impaired by TEA. CONCLUSIONS: From a hemodynamic point of view, TEA presents as a safe treatment option in sepsis or systemic inflammatory response syndrome.

Quantitative (1)H magnetic resonance spectroscopy of myoglobin de- and reoxygenation in skeletal muscle: reproducibility and effects of location and disease

1H-magnetic resonance spectroscopy ((1)H-MRS) of deoxymyoglobin (DMb) provides a means to noninvasively monitor the oxygenation state of human skeletal muscle in work and disease. As shown in this work, it also offers the opportunity to measure the absolute tissue content of DMb, the basic oxygen consumption of resting muscle, and the reperfusion characteristics after release of a pressure cuff. The methodology to determine these tissue properties simultaneously at two positions along the calf is presented. The obtained values are in agreement with invasive determinations. The reproducibility of the (1)H-MRS measurements is established for healthy controls and patients with peripheral arterial disease (PAD). A location dependence in axial direction, as well as differences between controls and patients are demonstrated for all parameters. The reoxygenation time in particular is expected to provide a means to quantitatively monitor therapies aimed at improving muscular perfusion in these patients.

Physiological effects of mechanical pain stimulation at the lower back measured by functional near-infrared spectroscopy and capnography

The aim was to investigate the effect of mechanical pain stimulation at the lower back on hemodynamic and oxygenation changes in the prefrontal cortex (PFC) assessed by functional near-infrared spectroscopy (fNIRS) and on the partial pressure of end-tidal carbon dioxide ( PetCO 2) measured by capnography. 13 healthy subjects underwent three measurements (M) during pain stimulation using pressure pain threshold (PPT) at three locations, i.e., the processus spinosus at the level of L4 (M1) and the lumbar paravertebral muscles at the level of L1 on the left (M2) and the right (M3) side. Results showed that only in the M2 condition the pain stimulation elicited characteristic patterns consisting of (1) a fNIRS-derived decrease in oxy- and total hemoglobin concentration and tissue oxygen saturation, an increase in deoxy-hemoglobin concentration, (2) a decrease in the PetCO 2 response and (3) a decrease in coherence between fNIRS parameters and PetCO 2 responses in the respiratory frequency band (0.2-0.5 Hz). We discuss the comparison between M2 vs. M1 and M3, suggesting that the non-significant findings in the two latter measurements were most likely subject to effects of the different stimulated tissues, the stimulated locations and the stimulation order. We highlight that PetCO 2 is a crucial parameter for proper interpretation of fNIRS data in experimental protocols involving pain stimulation. Together, our data suggest that the combined fNIRS-capnography approach has potential for further development as pain monitoring method, such as for evaluating clinical pain treatment.