EAL

HTN: Caffeine (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To investigate the acute effect of 250mg of caffeine on aortic stiffness in treated hypertensive subjects.

Inclusion Criteria:

Men and women with mild to moderate hypertension, who effectively controlled under medication in the past six months
Regular caffeine consumers.

Exclusion Criteria:

No exclusion criteria listed.

Description of Study Protocol:

Recruitment: Recruitment method was not described
Design: Randomized, placebo-controlled crossover trial
Blinding used: Double-blind
Intervention: 250mg caffeine (No-Doz) or placebo
Statistical analysis: Repeated-measures analysis of variance.

Data Collection Summary:

Timing of Measurements

After 12-hour overnight fast and rest period of 20 minutes, baseline measurements were taken
Caffeine or placebo was administered, then all measurements were repeated at 30, 60, 120, and 180 minutes afterwards.

Dependent Variables

Heart rate
Systolic blood pressure (BP)
Diastolic BP
Pulse pressure
Pulse wave velocity; carotid-femoral pulse wave velocity was calculated from measurements of pulse transit time and the distance traveled between two recording sites [pulse wave velocity = distance (in meters)/transit time (in seconds)], using a validated non-invasive device (Complior, Dupont Medical, Pantin, France) that allows online pulse wave recording and automatic calculation of pulse wave velocity. Two different pulse waves were simultaneously obtained at the base of the neck for the common carotid and over the right femoral artery with two transducers; the distance was defined at: (distance from the suprasternic notch to femoral artery) - (distance from carotid artery to suprasternic notch).

Independent Variables

250mg of caffeine or placebo
Subjects abstained from caffeine, alcohol and nicotine for at least 12 hours before each session.

Control Variables

None specified.

Description of Actual Data Sample:

Initial N: 12 subjects, seven men, five women
Attrition (final N): 12 assumed; not specified
Age: Mean age, 60±3 years
Ethnicity: Not specified
Other relevant demographics: None provided
Anthropometrics: Not applicable; crossover study
Location: Not clear where the study took place; editor/journal notes, "from the Medical Professorial Unit, St. Vincent's Hospital and Clinic, University of New South Wales, Sydney, Australia, and Athens Medical School, Hippokration Hospital, Athens, Greece."

Summary of Results:

Raw data not presented in article, other than summary graphs.

Variables	250mg Caffeine Effect Over Time and Statistical Significance from Baseline	Placebo Effect Over Time and Statistical Significance from Baseline	Statistical Significance Between Caffeine and Placebo Effect
Heart rate	Decreased 4.6 beats per minute, P=0.001	Decreased 2.5 beats per minute, P<0.005	Not significant
Systolic BP	Increased, P<0.001	Unchanged	P=0.005
Diastolic BP	Increased, P<0.05	Unchanged	Not significant
Pulse pressure	Increased, P<0.001	Unchanged	P<0.01
Pulse wave velocity	Increased, P<0.005	Unchanged	P<0.05

Other Findings

Pulse wave velocity exhibited an initial increase at 30 minutes, reached a peak at 60 minutes and dreased progressively thereafter, but without returning to baseline values at three hours.

Author Conclusion:

Caffeine exerts an acute unfavorable effect on aortic stiffness in treated hypertensive patients.

Funding Source:

University/Hospital:

University of New South Wales

Reviewer Comments:

Small sample size and incomplete information is provided on the participants (body weight, medication doses, definitions of "mild to moderate hypertension, how recruited, etc.)
Sample size is small with varying comorbidities among the participants (one with diabetes, two with hyperlipidemia), seemingly significant differences in family history (six with family history for premature vascular disease) and potential significant differences in lifestyle (smoking, alcohol use, etc.).

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	Yes
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	Yes

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	Yes
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	Yes
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		No
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	No
	2.2.	Were criteria applied equally to all study groups?	Yes
	2.3.	Were health, demographics, and other characteristics of subjects described?	No
	2.4.	Were the subjects/patients a representative sample of the relevant population?	???
3.	Were study groups comparable?		Yes
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	Yes
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	Yes
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	N/A
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	N/A
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	N/A
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		???
	4.1.	Were follow-up methods described and the same for all groups?	N/A
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	???
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	???
	4.4.	Were reasons for withdrawals similar across groups?	???
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		Yes
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	Yes
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	Yes
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	N/A
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	N/A
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	Yes
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	N/A
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	Yes
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	N/A
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	Yes
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	Yes
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		Yes
	7.1.	Were primary and secondary endpoints described and relevant to the question?	Yes
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	N/A
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	Yes
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	Yes
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	???
	7.7.	Were the measurements conducted consistently across groups?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		Yes
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	Yes
	8.2.	Were correct statistical tests used and assumptions of test not violated?	Yes
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	Yes
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	N/A
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	N/A
	8.6.	Was clinical significance as well as statistical significance reported?	Yes
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	N/A
9.	Are conclusions supported by results with biases and limitations taken into consideration?		No
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	No
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	No
	10.2.	Was the study free from apparent conflict of interest?	Yes