A highly sensitive colorimetric determination of serum zinc using water-soluble pyridylazo dye

A colorimetric method for precise and accurate determination of zinc in serum is presented. Only 0.3 ml of sample is necessary, because of the use of a new, highly sensitive reagent, 2-(5-bromo-2-pyridylazo)-5-(N-n-propyl-N-3-sulfopropylamino)-phenol ($\text{?}{}_{\mathrm{<mtext>554</mtext><mtext>nm</mtext>}}\text{= 1.3 × 10}{}^5\text{1 ·}\text{mol}{}^{\mathrm{?1}}\text{·}\text{cm}{}^{\mathrm{?1}}$), which is water-soluble and has long-term stability. Interference of iron and copper in serum can be removed by co-precipitation of the iron fluoride complex with trichloroacetic acid precipitated proteins and the copper dithiocarboxy sarcosine complex, respectively. Within-run and day-to-day precision (CV) are in the range of 0.3–3.5% and 1.9–3.1%, respectively, depending on the serum zinc content. A good correlation (r = 0.98, p < 0.05) was obtained between this method and atomic absorption spectrometry. In contrast to previous colorimetric methods, the present method does not involve heating, extraction with organic solvents, or a cyanide masking system.     

Methodology for the detection and quantitation of delta9-tetrahydrocannabinol in plasma by dansylation and double labelling.

A practical method for the detection and quantitation of $\text{Δ}{}^9$-tetrahydro-cannabinol ($\text{Δ}{}^9$-THC) in plasma is presented. This method is based on combined dansylation and double labelling techniques. $\text{Δ}{}^9$-THC is detected as its [methyl-¹⁴C]dansyl derivative. Addition of $\text{[}{}^3\text{H]Δ}{}^9$-THC as internal standard allows correction for incomplete dansylation, extraction and purification losses.The experimental process involves: addition of $\text{[}{}^3\text{H]Δ}{}^9$-THC, extraction of $\text{Δ}{}^9$-THC and $\text{[}{}^3\text{H]Δ}{}^9$-THC using a suitable organic solvent system followed by a selective extraction of phenols with modified Claisen's alkali, esterification by addition of [methyl-¹⁴C]dansyl chloride ([¹⁴C]DANS-Cl), purification by one or two-dimensional thin-layer chromatography and measurement of ¹⁴C and ³H. A study was conducted to define esterification reaction parameters: temperature and time reaction, [¹⁴C]DANS-Cl excess, pH, nature, volume and molarity of the buffer. These findings showed that the yield of esterification depended above all on DANS-Cl excess and varied with three zones. These variations did not allow to obtain a linear response. Consequently, it was impossible to refer to a calibration plot and it was necessary to incorporate $\text{[}{}^3\text{H]Δ}{}^9$-THC whose comportment identity with inactive $\text{Δ}{}^9$-THC was checked. The use of dansylation and double labelling techniques provides a sensitive method for quantitation of $\text{Δ}{}^9$-THC with 2.5 ng sensitivity per tube and 10% reproductibility.     

Studies on the radioiodination of very low density lipoprotein obtained from different mammalian species

Very low density lipoprotein (VLDL) isolated from human, pig and rat serum showed marked differences in labelling patterns when radioiodinated under similar conditions, with greater amounts of ¹²⁵ I-labelled iodine being incorporated into the lipid moieties of pig and rat VLDL than into human VLDL. The effect (on their biological behaviour) of introducing increasing amounts of iodine into the lipoproteins was tested for both human and rat VLDL with preparations containing iodine:protein (I/P) ratios varying from < 0.5 to 12. After injection into rats and analysis of disappearance curves, only minor differences in catabolic rates were observed between different preparations. Thus, rat VLDL, with I/P ratios varying from < 0.5–12 showed fast and slow exponential components varying in half life ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) between 40–63 min and 10–11 h, respectively, while human VLDL with comparable I/P ratios, had a fast component varying from ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) 50–78 min and a slower component ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) of 10.5–12.5 h The plasma disappearance of human VLDL, labelled by the lactoperoxidase method, was also characterised by two exponential components with mean half lives of 67 min and 11 h, respectively, suggesting similarity in the biological behaviour of human VLDL labelled both enzymatically and with iodine monochloride. The results also indicated similarity in the catabolism of rat and human VLDL by the rat, suggesting that this animal is a suitable model for studying VLDL metabolism.     

Infinite dilution conductimetry of plasma and urine: Correlation with osmolality

The infinite dilution conductivity (IDC) of plasma ajid urine allows a measurement of the electrolyte content in small samples (5 to 15 μl). The method was compared to the corrected osmolality (Π′_p) measured by the freezing-point depression. A linear correlation existed between Π′_p and the IDC:

$\text{for plasma}\text{: Π′}{}_{\mathrm{<mtext>p</mtext>}}\text{= 13.10 σ}{}_{\mathrm{<mtext>o,p</mtext>}}\text{+ 37.00 (n = 46}\text{and}\text{r = 0.9949)}$

$\text{for urine}\text{: Π′}{}_{\mathrm{<mtext>u</mtext>}}\text{= 12.75σ}{}_{\mathrm{<mtext>o,u</mtext>}}\text{+ 16.56 (n = 85}\text{and}\text{r = 0.9504)}$

The measurement of the IDC does not depend on protein concentration and can be used instead of the osmometer methods to determine the total plasma and urine electrolyte content.     

Asphyxia,cardiac arrest and resuscitation in rats. I. Short term recovery

This study was conducted to investigate the degree of insult from asphyxia leading to total body circulatory arrest, as a model for brain resuscitation studies in rats.Of 78 male rats, 68 were anesthetized with halothane in $\text{0}{}_2\text{N}{}_2\text{0}$, controlled ventilated, paralyzed with pancuronium and asphyxiated, 5, 7.5, 10, 12.5 and 15 min, respectively. Asphyxiation led to circulatory arrest in 244 ± 22 s (mean ± S.E.M.). Resuscitation was successful in 65% within 60 s using controlled ventilation with 100% 02, extrathoracic compressions and epinephrine intravenously. Subsequent intensive care to 6, 12 or 24 h was successful in 50% of resuscitated rats.At 6, 12 and 24 h of recovery, neurologic deficit scores and light microscopic neuropathology scores of the brain after in vivo fixation of the total body with intraventricular paraformaldehyde 3%, revealed a large scatter variability without a clear pattern. Lesions were located mostly in the frontal cortex and hippocampus (footplate) with ischemic neuronal change as the most frequent structural change. Brain cell necrosis was not seen after successful resuscitation. It seems that both scores were influenced by postinsult stress, as indicated by paroxysmal hypertension and motor activity, by complications, such as obstruction of the tracheotomy cannula by abundant sputum production, and by partial sedation with N₂O and paralysis with pancuronium.This study indicates the feasibility of an asphyxial insult in rats for use in resuscitation studies of short duration. Although 24 h post-insult recovery is possible, up to 6 h seems most practical, with asphyxia of 7.5–10 min most successful and controllable. Questions are raised about the effects of irritation during the post-insult intensive care on both neurological deficit and neuropathology scores.     

Prevention of heart failure in dogs during arterial hypoxaemia by means of intra-aortic balloon pumping

In dogs intra-aortic balloon pumping (IABP) under control conditions resulted in a significant decrease of cardiac and stroke work index, systolic aortic pressure, and diastolic aortic pressure, and $\text{d}\text{p}\text{d}\text{t}{}_{\mathrm{<mtext>max</mtext>}}$. After continuous circulatory breakdown during cardiogenic shock conditions the progressive fall in arterial blood pressure,$\text{d}\text{p}\text{d}\text{t}$ values, and stroke volume, and the continuous rise in left ventricular end diastolic pressure and pulmonary artery pressure was interrupted by means of IABP, and values remained at their levels for the period of observation for 20 min or were slightly improved. In contrast, interruption of IABP resulted in circulatory breakdown within 2–7 min. However, repetitive IABP treatment, started early enough with an arterial pressure above 60-mmHg, was able to restore cardiac haemodynamics in most instances. In accordance with other investigators, we conclude that IABP reduced the energy demand of myocardium. However, maximal benefit of this cirulatory assistance device can be expected only if IABP is initiated early enough.     

Estimation of Jones matrix,birefringence and entropy using Cloude-Pottier decomposition in polarization-sensitive optical coherence tomography: erratum

An erratum is presented to correct errors in the equations in [Biomed. Opt. Express 7(9), 3551–3573 (2016)].OCIS codes: (110.4500) Optical coherence tomography, (170.4500) Optical coherence tomography, (170.4470) Ophthalmology, (120.2130) Ellipsometry and polarimetryIn our paper [1], several errors in the equations have been found and are corrected as below.Equation (22) of [1] should read Hnoise(Ei¯)=∑j=12−ζj(i)log4(ζj(i)),(22) where the negative sign and the base 4 of the logarithm were described correctly. We note that the same base of the logarithm has to be used for the entropy throughout the processing flow.In addition, Eq. (28) was erroneously presented in [1], which algebraically resulted in 1 regardless of the signals and noises. It was related to the erroneous definition of Eq. (27) in [1]. Equation (27) should be defined to include the bias of the noises as [s0″(1)s1″(1)s2″(1)s3″(1)]:=[|g1H|2¯+|g1V|2¯|g1H|2¯−|g1V|2¯2Re[g1Hg1V*¯]2Im[g1Hg1V*¯]]=[|g1H|2¯+|g1V|2¯|g1H|2¯−|g1V|2¯2Re[E1HE1V*¯]2Im[E1HE1V*¯]]=[|g1H|2¯+|g1V|2¯|g1H|2¯−|g1V|2¯2|E1H|¯|E1V|¯cosδ2|E1H|¯|E1V|¯sinδ]=[|g1H|2¯+|g1V|2¯|g1H|2¯−|g1V|2¯2|g1H|2¯−|n1H|2¯|g1V|2¯−|n1V|2¯cosδ2|g1H|2¯−|n1H|2¯|g1V|2¯−|n1V|2¯sinδ],(27) which is based on Eq. (25) of [1]. Equation (28) of [1] should then read P(1)={s1″(1)}2+{s2″(1)}2+{s3″(1)}2s″0(1)=(|g1H|2¯−|g1V|2¯)2+4(|g1H|2¯−|n1H|2¯)(|g1V|2¯−|n1V|2¯)|g1H|2¯+|g1V|2¯.(28)Consequently, Eqs. (43)-(46) of [1] should readP(ε1¯)=(|ε1H|2¯−|ε1V|2¯)2+4(|ε1H|2¯−Var(ε1H))(|ε1V|2¯−Var(ε1V))|ε1H|2¯+|ε1V|2¯,(43)P(ε2¯)=(|ε2H|2¯−|ε2V|2¯)2+4(|ε2H|2¯−Var(ε2H))(|ε2V|2¯−Var(ε2V))|ε2H|2¯+|ε2V|2¯,(44)P(ε1¯|ε2¯)=(|ε1H|2¯−|ε1V|2¯)2+4(|ε1H|2¯−Var(ε1H|ε2¯))(|ε1V|2¯−Var(ε1V|ε2¯))|ε1H|2¯+|ε1V|2¯,(45)P(ε2¯|ε1¯)=(|ε2H|2¯−|ε2V|2¯)2+4(|ε2H|2¯−Var(ε2H|ε1¯))(|ε2V|2¯−Var(ε2V|ε1¯))|ε2H|2¯+|ε2V|2¯.(46)In Eq. (28), |g1H|2¯−|n1H|2¯ and |g1V|2¯−|n1V|2¯ should be non-negative in principle, but can be negative in practice. If these parameters are negative in the data processing, they are set as zero to avoid physically undefined values of P⁽¹⁾. Similar operations are also applied to Eqs. (43)-(46).In addition, the last sentence of Section 2.5 shown in the following should be deleted because it was presented incorrectly and did not make sense in [1]; “The absolute-squared expected values of the matrix elements in Eq. (24) or (29) that are used in Eqs. (35)-(42) are calculated as |g1H|2¯−|n1H|2¯ and similarly for all other elements.”Since all of the equations were correctly implemented in our processing software of [1], no change is required in the results.     

Mechanized determination of the apparent unbound unconjugated bilirubin concentration in serum.

The peroxidase method for determining the apparent unbound bilirubin concentration in serum has been automated by use of a programmable, computer-directed spectrophotometer. This mechanized assay determines the total bilirubin concentration and apparent unbound bilirubin concentration in serum samples and titrates the serum with bilirubin to estimate the effect of increasing total bilirubin concentrations on the apparent unbound bilirubin concentration. The entire analysis requires 0.1 mL of serum and 4 min operation time, as compared with about 30 min for the manual method. The coefficients of variation for determination of the apparent unbound bilirubin concentration in bilirubin-enriched commercial control serum were 2.8% within-day and 5.6% between-day. Bilirubin--albumin binding in serum samples from infants with severe hyperbilirubinemia was analyzed by the manual peroxidase method, the automated peroxidase method, and Sephadex gel filtration. Good correlation was found among all three methods.     

Neuraminidase activity in the mucolipidoses (types I,II and III) and the cherry-red spot myoclonus syndrome

Two neuraminidase (EC 3.2.1.18) components, A and B, were distinguished in cultured skin fibroblasts on the basis of thermolability at 37°C. The more labile component (A) $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 4.7–5.3}\text{min}$ at 37°C, comprises 66–90% of total neuraminidase activity when determined using sodium ($\text{4-}\text{methylumbelliferyl}\text{-α-}\text{d}\text{-N-}\text{acetylneuraminate}$) (MU-α-N) as substrate. Activity was assayed at 0°C for 18 h instead of 37°C to fully determine both thermolabile and thermostable components. Diminished activity was noted in cultured fibroblasts from mucolipidoses I, II and III (MLI, MLII, MLIII) and the cherry-red spot myoclonus syndrome (CRSM) patients when assayed at both 0 and 37°C with either MU-α-N or each of a series of α(2 → 3)- and α(2 → 6)-linked N-acetylneuraminyl-oligosaccharides. Increased sensitivity and rapidity of analyses were achieved using MU-α-N as substrate in determining neuraminidase activity. Results from two obligate heterozygote MLI cell lines (14.5 and 8.0% of control activity) indicate that the MU-α-N substrate could be useful for heterozygote detection.     

Analysis of ventilatory ratio as a novel method to monitor ventilatory adequacy at the bedside

Introduction

Due to complexities in its measurement, adequacy of ventilation is seldom used to categorize disease severity and guide ventilatory strategies. Ventilatory ratio (VR) is a novel index to monitor ventilatory adequacy at the bedside. VR=(V˙Emeasured×PaCO2measured)/(V˙Epredicted×PaCO2ideal). V˙Epredicted is 100 mL.Kg^-1.min^-1 and Pa_{CO2 ideal} is 5 kPa. Physiological analysis shows that VR is influenced by dead space (V_D/V_T) and CO2 production (V˙CO2). Two studies were conducted to explore the physiological properties of VR and assess its use in clinical practice.

Methods

Both studies were conducted in adult mechanically ventilated ICU patients. In Study 1, volumetric capnography was used to estimate daily V_D/V_T and measure V˙CO2 in 48 patients. Simultaneously, ventilatory ratio was calculated using arterial blood gas measurements alongside respiratory and ventilatory variables. This data was used to explore the physiological properties of VR. In Study 2, 224 ventilated patients had daily VR and other respiratory variables, baseline characteristics, and outcome recorded. The database was used to examine the prognostic value of VR.

Results

Study 1 showed that there was significant positive correlation between VR and VD/VT (modified r = 0.71) and V˙CO2 (r = 0.14). The correlation between VR and V_D/V_T was stronger in mandatory ventilation compared to spontaneous ventilation. Linear regression analysis showed that V_D/V_T had a greater influence on VR than V˙CO2 (standardized regression coefficient 1/1-V_D/V_T: 0.78, V˙CO2: 0.44). Study 2 showed that VR was significantly higher in non-survivors compared to survivors (1.55 vs. 1.32; P < 0.01). Univariate logistic regression showed that higher VR was associated with mortality (OR 2.3, P < 0.01), this remained the case after adjusting for confounding variables (OR 2.34, P = 0.04).

Conclusions

VR is an easy to calculate bedside index of ventilatory adequacy and appears to yield clinically useful information.     

Substrates for the assay of α-l-iduronidase

Procedures are described for the preparation of two disaccharides, 4-O -α -L-iduronosyl-2, 5-anhydro[³H]mannitol and $\text{3-O-α-}\text{l}\text{-iduronosyl}\text{-2,5--}\text{anhydro}\text{[}{}^3\text{H]-talitol}$, from heparin and dermatan sulfate, respectively. These disaccharides lend themselves to an easy assay of α-L-iduronidase which is based on the fractionation of the liberated neutral anhydro[³H]mannitol or anhydro[³H]talitol from the unreacted substrate by adsorption of the latter to Dowex 1.Investigation of the reaction conditions showed that the α-L-iduronidase activity (enzyme from human fibroblasts and Helix pomatia) was optimal at pH 3.6 in acetate buffer containing 0.01 M NaCl with iduronosyl-2,5-anhydro[³H]mannitol as substrate. For iduronosyl-2,5-anhydro[³H]talitol the pH optimum was 4.0 with the H. pomatia enzyme.The K_m for iduronosyl-2,5-anhydro[³H]mannitol was 0.23 mM with human fibroblasts and 0.04 mM with Helix enzyme; a KM value of 0.02 mM was determined for iduronosyl-2,5-anhydro[³H]talitol with the Helix α-l-iduronidase.     

Measurement of the reduced scattering coefficient of turbid media using single fiber reflectance spectroscopy: fiber diameter and phase function dependence

This paper presents a relationship between the intensity collected by a single fiber reflectance device (R_SF) and the fiber diameter (d_fib) and the reduced scattering coefficient ( μs′) and phase function (p(θ)) of a turbid medium. Monte Carlo simulations are used to identify and model a relationship between R_SF and dimensionless scattering ( μs′dfib). For μs′dfib > 10 we find that R_SF is insensitive to p(θ). A solid optical phantom is constructed with μs′ ≈ 220 mm−1 and is used to convert R_SF of any turbid medium to an absolute scale. This calibrated technique provides accurate estimates of μs′ over a wide range ([0.05 – 8] mm⁻¹) for a range of d_fib ([0.2 – 1] mm).OCIS codes: (300.6550) Spectroscopy, visible; (280.1350) Backscattering; (060.2310) Fiber optics; (290.7050) Turbid media; (170.3660) Light propagation in tissues     

Creatine kinase B-subunit activity in human serum. I. Development of an immunoinhibition method for routine determination of S-creatine kinase B-sununit activity

The properties of an inhibiting antibody directed against the M-subunits of human creatine kinase (EC 2.7.3.2, CK) were investigated in the reaction system recommended by the Scandinavian Committee on Enzymes (S.C.E.).At 37° C the rate of immunoinhibition of human CK M-subunit dependent activity corresponded to a $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of 38 s giving a k value of ?2 per cent · s^?1 when samples were incubated in the S.K.E. CK reagent A in the presence of antibody. Under the selected conditions immunoinhibition of S-CK M-subunit activity up to 1800 U/l was 99 per cent completed within 5 minutes using undiluted samples. No inhibition of CK B-subunit activity occurred at the chosen concentration of antibody. The inhibition data were verified using human sera and electrophoretically homogeneous preparations of human CK isoenzymes BB and MM.Sample adenylate kinase (EC 2.7.4.3, AK) was found to constitute a potential source of falsely increased S-CK B activity. As reported in the accompanying paper a S-CK B value of 15 U/l was used as a discrimination value in the diagnosis of acute myocardial infarction. The S.C.E. CK method incorporates a combination of two AK inhibitors adenosine 5'-monophosphate and P¹, P⁵-diadenosine 5'-pentaphosphate. However, a frequency analysis of sample AK activities demonstrated that AK activities of more than 8 U/l will occur in about 10 per cent of the cases. Consequently, it was deemed necessary to measure the individual sample blank AK rates.The routine procedure developed thus included three separate measurements: determination of total S-CK and of S-CK B activities in the absence and presence of antibody, respectively. As the immunoinhibition was only 99 per cent complete a value corresponding to one per cent of the total S-CK activity was subtracted from the measured S-CK B activity. Likewise, the individual sample AK activity had to be measured and subtracted from the apparent S-CK B activity.The within-series precision of this S-CK B method at the levels of 10 U/l and 20 U/l corresponded to C.V. values of 10 and 5 per cent, respectively. Day-to-day precision at the level of 417 U/l corresponded to a C.V. of 4 per cent. The day-to-day precision of a control, total CK activity 625 U/l, gave a mean value of 53% ± 3% of CK B activity.     

Optical theorem for acoustic non-diffracting beams and application to radiation force and torque: erratum

We correct minor errors in four equations in our recent paper [Biomed. Opt. Express 4(9), 1610–1617 (2013)]. They are equations (11), (14), (15), and (17) therein, where a factorial ratio (n−m)!(n+m)! was mistakenly omitted. All the other equations and analysis in the paper were correct.OCIS codes: (350.4855) Optical tweezers or optical manipulation, (290.2200) Extinction, (290.4020) Mie theory, (290.5850) Scattering, particlesWe correct a factor (n−m)!(n+m)! that was mistakenly omitted in four equations in our recent paper [1]. They are Eqs. (11), (14), (15), and (17) in [1]. The correct versions of these four equations respectively are, σext=πk2∑n=|m|∞(2n+1)(n−m)!(n+m)![Pnm(cosβ)]2Re[2(1−sn)],(11) Qsca≡σsca/(πa2)=1(ka)2∑n=|m|∞(2n+1)(n−m)!(n+m)![Pnm(cosβ)]2(|sn−1|2),(14) Qabs≡σabs/(πa2)=1(ka)2∑n=|m|∞(2n+1)(n−m)!(n+m)![Pnm(cosβ)]2(1−|sn|2).(15) Qext,sca=σext,sca/(πa2)=4(ka)2∑n=|m|∞(2n+1)(n−m)!(n+m)![Pnm(cosβ)]2sin2(δn).(17)These equations were correctly given in our earlier paper [2]; they are equations (16)–(18) in [2]. Note also that cosβ is sometimes denoted by b. All the other equations and analysis in [1] were correct and are unaffected by this correction.     

Investigation of depth-resolved nanoscale structural changes in regulated cell proliferation and chromatin decondensation: erratum

We correct minor errors in two equations reported in our paper [Biomed. Opt. Express 4, 596–613 (2013)]; an additional factor of two was mistakenly incorporated in Eqs. (3) and (4). We give the correct equations below. All the simulations and experiments in the previous paper were performed using the correct equations, and therefore, remain the same.OCIS codes: (180.3170) Interference microscopy, (300.6300) Spectroscopy, Fourier transforms, (170.4730) Optical pathology, (170.1610) Clinical applicationsWe correct Eqs. (3) and (4) in our previous paper [1] by removing the factor of two that was mistakenly incorporated in both of them. The correct versions of Eqs. (3) and (4) respectively are,p(zopl)=2Γ⊗[(Rr+Rs)δ(0)+2rrℱ−1(∫0Zrs(z'')cos(4πK2n(z'')z'')dz'')](zopl),(3)and,δp(zopl)=λ02πarctan(Im(p(zopl))Re(p(zopl))) ,zopl≠0.(4)In Eq. (3), the convolution argument has been changed from 2z_opl to z_opl, and in Eq. (4), the factor of two has been removed from the denominator. The reason for the deletion, also explained in our original paper [1], is that the factor of two is implicitly incorporated within the spatial frequency K = (k_s – k _i)/2π = 2(k/2π) z = (k/π) z, under the normal illumination and collection geometry for the common-path setup, thereby allowing us to directly perform the Fourier transform at the optical depth location of z_opl. The simulation and experimental results reported in the paper remain unaltered, as they were performed using the correct equations.     

High-Intensity Walking Time Is a Key Determinant to Increase Physical Fitness and Improve Health Outcomes After Interval Walking Training in Middle-Aged and Older People

ObjectiveTo examine the effects of interval walking training (IWT) on the estimated peak aerobic capacity (e$\dot{V}{\text{O}}_{2\text{peak}}$) and lifestyle-related disease (LSD) score while focusing on exercise intensity and volume in middle-aged and older people.Participants and MethodsMen and women (N=679; mean age, 65±7 SD years) completed 5-month IWT. Participants were instructed to repeat 5 or more sets of fast and slow walking for 3 minutes each at 70% or more and 40% e$\dot{V}{\text{O}}_{2\text{peak}}$ for walking, respectively, per day for 4 or more d/wk. This study was conducted from April 1, 2005, through February 29, 2008.ResultsInterval walking training increased e$\dot{V}{\text{O}}_{2\text{peak}}$ by 14% and decreased LSD score by 17% on average (P<.001). During 5-month IWT, fast and slow walking times were 88±65 SD and 100±86 min/wk, respectively, but varied among participants. We divided participants into approximately 10 bins for 6 minutes each of fast and slow walking times per week up to 60 min/wk, and above this time, approximately 8 bins for 30 or 60 minutes each of fast and slow walking up to the maximal time. We found that both e$\dot{V}{\text{O}}_{2\text{peak}}$ and LSD score improved as fast walking time per week increased up to 50 min/wk (R²=0.94; P<.001 for e$\dot{V}{\text{O}}_{2\text{peak}}$; R²=0.51; P=.03 for LSDS) but plateaued above this time. In contrast, improvement in neither e$\dot{V}{\text{O}}_{2\text{peak}}$ nor LSDS was positively correlated with slow or total walking time per week. Multiple regression analyses confirmed that fast walking time per week was the major determinant of improvements in e$\dot{V}{\text{O}}_{2\text{peak}}$ (P<.001) and LSD score (P=.001).ConclusionHigh-intensity walking time during IWT is a key factor to increase e$\dot{V}{\text{O}}_{2\text{peak}}$ and decrease LSD score in middle-aged and older people.